Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

Synthesis and characterization of transition-metal germanides

Xie, Y.; Yuan, Y.; Hübner, R.; Wang, M.; Helm, M.; Zhou, S.; Prucnal, S.

Si was sufficient to fulfil the requirements of microelectronic industry for more than five decades. Further progress based on the miniaturisation of transistors is challenging. Therefore new materials and concepts are considered for the next generation of nanoelectronics. In this work, we present the formation of transition-metal germanides epitaxially grown on Ge wafer. Those materials have great promise for both the ohmic contacts to n-type Ge with extremely low specific contact resistivity and spintronics. The transition-metal germanides are synthesized by metal sputtering on Ge followed by millisecond range flash lamp annealing which is suitable for larger-area fabrication and compatible with CMOS technology. On one hand, orthorhombic NiGe whose contact resistivity is only around 1.2×10-6 Ω cm2, is beneficial for achieving high-performance Ge-based nano-electronic devices. On the other hand, cubic FeGe with B20 phase is a Skyrmion-carrier material attractive for spintronics. In summary, the epitaxial transition-metal germanides materials can be obtained by a novel epitaxial approach which provides insight to their technological usage.

Keywords: transition-metal germanides; spintronics

  • Poster
    2018 DPG Spring Meeting Berlin, 12.03.2018, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-28562
Publ.-Id: 28562


Ultra-fast solid phase epitaxy of Mn5Ge3 on (001) Ge substrate

Xie, Y.; Yuan, Y.; Hübner, R.; Wang, M.; Xu, C.; Grenzer, J.; Helm, M.; Zhou, S.; Prucnal, S.

In the present work, we report on epitaxial growth of ferromagnetic Mn5Ge3 thin films on (001) Ge substrates induced by Mn in-diffusion during non-equilibrium flash lamp annealing for 20 ms. The ferromagnetic Mn5Ge3/Ge samples with very sharp interface between the Mn5Ge3 layer and the Ge substrate can be used to fabricate spintronic devices. Temperature-dependent magnetization reveals a Curie temperature of 282 K which can be tuned much above room temperature by strain engineering and/or co-doping with C. The microstructural properties of the fabricated films were investigated by X-ray diffraction, cross-sectional TEM and Rutherford backscattering spectrometry. Both used material and technology are highly compatible with complementary metal-oxide-semiconductor (CMOS) technology and can be used for spintronics.

Keywords: Epitaxial growth; ferromagnetic; flash lamp annealing

  • Poster
    2018 EMRS Spring Meeting Strasbourg, 18.06.2018, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-28561
Publ.-Id: 28561


Challenges of the Circular Economy: A Material, Metallurgical, and Product Design Perspective

Reuter, M.; van Schaik, A.; Gutzmer, J.; Bartie, N.; Abadías-Llamas, A.

Circular economy’s (CE) noble aims maximize resource efficiency (RE) by among others extending product life cycles and using wastes as resources. Modern society’s vast and increasing amounts of waste and consumer goods, their complexity and functional material combinations is challenging the viability of the CE in spite of various alternative business models promising otherwise. The metallurgical processing of CE enabling technologies requires in the end a sophisticated and agile metallurgical infrastructure. The challenges of reaching a CE will among others be highlighted in terms thermodynamics, transfer processes, technology platforms, digitalization of the processes of the CE stakeholders, design for recycling (DfR) based on a product (mineral)-centric approach, challenging material centric considerations. Integrating product centric considerations into the water, energy, transport, heavy industry, and other smart grid systems will maximize the RE of future smart sustainable cities, providing the fundamental detail for realizing and innovating the United Nation’s Sustainability Development Goals.

Keywords: Circular economy; Process metallurgy; Thermoeconomics; Exergy; Design for Recycling

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-28559
Publ.-Id: 28559


The Geo-metallurgy of the circular economy: Fairphone

Reuter, M. A.

tools - HSC Sim & GaBi LCA
Particle description of recycling systems inclusive of exergy & energy
Recycling
Analysis of systems: Rock, residue, recyclate to refined metal
Copper production system: Irreversibility analysis of system & Footprint of complete system
Bill-of-Materials & Full Material Declaration linked to metallurgy, alloy and materials production

Keywords: HSC Sim; GaBi LCA; recycling systems; exergy; energy; Recycling

  • Invited lecture (Conferences)
    International Mineral Processing Congress, 17.-21.09.2018, Moskau, Russland

Permalink: https://www.hzdr.de/publications/Publ-28558
Publ.-Id: 28558


Thermodynamic evaluation using the law of mass action under consideration of the activity coefficients in the system NdCl3-HCl (or NaOH)-H2O-DEHPA-kerosene

Scharf, C.; Ditze, A.

For the recovery of neodymium, an important rare earth metal, solvent extraction using DEHPA as extractant is a possible process for winning and recycling. A preceding study by the authors has provided extensive experimental data of the system neodymium-chloride-hydrochloric acid (or sodium hydroxide)-water-di-(2-ethylhexyl)phosphoric acid (DEHPA)-kerosene. It was found that the description of the reaction Nd3+ + 3 (DEHPA)2 <=> Nd(DEHP·DEHPA)3 + 3 H+ by an ideal mass action law is only partly satisfactory. This article investigates the contribution of several parameters to non-ideality. On this basis, expressions for activity coefficients of neodymium in the aqueous phase as well as DEHPA and neodymium in the organic phase are derived. The resulting equations are shown to represent the system with considerably better accuracy than previously possible.

Keywords: thermodynamic evaluation; solvent extraction; neodymium; DEHPA

Permalink: https://www.hzdr.de/publications/Publ-28557
Publ.-Id: 28557


CIRCULAR ECONOMY STRATEGIES - Responsible Business Practices // Process Model Based Footprints Using HSC Chemistry Software

Reuter, M. A.; Roine, A.

SusCritMat aims to educate people from Master’s student level up, both in industry and academia about important aspects of Sustainable critical raw materials. In a novel concept, it introduces courses on these complex and interdisciplinary topics in a modula structure, adaptable to a variety of different formats and accessible to both students and managers in industry. These courses will develop new skills which will help participants to better understand the impact and role of critical raw materials in the whole value chain; enabling them to identify and mitigate risks. Understanding the bigger picture and the interconnected nature of global business and society is increasingly necessary to and valued by industry. SusCritMat is an EU-funded project that brings together the technical and pedagogical expertise of leading educational institutions and business partners. It uses and creates teaching materials which can be combined into different course formats. Multi-media education materials will be made available to participants of summer and winter schools so that they can work with state-of-the-art techniques and data.

Keywords: Circular Economy; resource efficiency; sustainability; Digitalization; Simulation

  • Lecture (others)
    SusCritMat Autumn School for Professionals 2018, 24.-26.10.2018, Delft, Niederlande

Permalink: https://www.hzdr.de/publications/Publ-28556
Publ.-Id: 28556


Interface reactions of differently coated carbon-bonded alumina filters with an AZ91 magnesium alloy melt

Schramm, A.; Bock, B.; Schmidt, A.; Zienert, T.; Ditze, A.; Scharf, C.; Aneziris, C. G.

To investigate possible reactions between differently coated carbon-bonded alumina filters and an AZ91 magnesium alloy melt, immersion tests were carried out. Uncoated as well as MgAl2O4-, Al2O3-, nano- (carbon nano tubes/alumina nano sheets) and MgO-C-coated filters were tested. Thermodynamic calculations showed that only magnesia (MgO) and carbon are stable against molten magnesium; alumina (Al2O3) and spinel (MgAl2O4) will be reduced under the formation of magnesia. Optical and scanning electron microscopy as well as EDX analysis were performed near and at the filter-magnesium alloy-interface of the cooled and sectioned filter samples after their immersion into the AZ91 melt. The results of the thermodynamic calculations were confirmed by the experiments. The MgO-C-coated filter was the only one that did not show an in situ-formed layer on its surface after being in contact with the magnesium alloy melt. The alumina- or spinel-containing filter surfaces displayed platelet-like in situ layers after their contact with the molten AZ91. The results of the EDX analysis of these layers suggest their composition of MgO, since notable respective Mg and O contents were detected, as predicted by the calculations.

Keywords: Ceramic Foam Filter; Interfaces; Al2O3; MgO

Permalink: https://www.hzdr.de/publications/Publ-28555
Publ.-Id: 28555


Semi-Solid remelting of Magnesium-Chips

Ohmann, S.; Ditze, A.; Scharf, C.

Compact and loose magnesium chips were processed by means of remelting. The remelting was successfully performed using the new method of semi-solid melting, without the addition of flux, at temperatures between 580°C and 600°C. In this temperature range, the exothermic reaction between magnesium and the oxygen present in the surrounding atmosphere is avoided; in addition, the oxygen layer of the chips is stripped off by the particles of the semi-solid melt. Results show that more than 95% of the magnesium chips can be recovered as metal. Experiments were performed on different scales to obtain production parameters for the recycling process. Larger particle sizes of magnesium chips can be remelted faster than smaller ones. The ability to remelt at temperatures in the semi-solid region of alloys demonstrates the possibility of recovering virtually all of the metal from the chips.

Permalink: https://www.hzdr.de/publications/Publ-28554
Publ.-Id: 28554


System integration, Environmental impact and Business models

Reuter, M. A.

Determine economic feasibility (OPEX and CAPEX) for industrial scale pretreatment based on different energy sources and their integration with existing industrial production of Mn-alloys for different cases;
Prepare a business plan for implementation of pretreatment technology at the project partners;
Prepare a strategy for future exploitation of the developed technology outside the project consortium and identify how this will reduce CO2 emissions also by including the embodied energy of the system;
Assess environmental impact on manganese alloy production, especially effect on CO2 emission and energy consumption of industrial scale pretreatment in separate unit integrated with existing industrial Mn-alloy production. This will be estimated by linking system simulation with environmental footprint using LCA and Life Cycle Cost analysis tools; and
Maximize the resource efficiency of manganese production by optimising the processing and the infrastructure of the system of technologies. This will be based on applied scales for mass flows and production processes. Both energy and exergy efficiency will be maximized.

Keywords: energy efficiency; exergy efficiency; resource efficiency

  • Lecture (others)
    PreMa Project Meeting, 22.-23.10.2018, Trondheim, Norwegen
  • Lecture (others)
    PreMa Projekt Meeting, 13.-14.11.2019, Oberursel, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28553
Publ.-Id: 28553


Multi-source hyperspectral imaging of carbonatite-hosted REE-Nb-Ta mineralization at Marinkas Quellen, Namibia

Booysen, R.; Zimmermann, R.; Lorenz, S.; Gloaguen, R.; Nex, P. A. M.

The demand for mineral and metalliferous resources needs to match the continued global rise in population and global economic growth. Rare Earth Elements (REEs), Niobium (Nb) and Tantalum (Ta) are such deposits in high demand. This global rise makes it difficult to meet the growing demand using only the currently available resources, such as recycled REEs and known REE deposits. Although the concept of a purely circular economy is very attractive through the use of recyclable REE-Nb-Ta, this model is not completely sustainable due to the increased energy needed to bolster such a model. Therefore, a renewed focus on the exploration of REE-Nb-Ta deposits is imperative to ensure the future development of this commodity.
Traditional exploration techniques are mainly based on extensive field work supported by geophysical surveying. Restrictions such as field accessibility, financial status, area size and climate can hinder these traditional exploration techniques. Hence, we suggest to increase the use of multi-source and multi-scale hyperspectral remote sensing in order to decrease conventional restrictions in the exploration of minerals through the use of aerial and ground-based methods. The multi-scale, multi-source approach will consist of a downscaling procedure, moving from low spatial resolution to high spatial resolution. Firstly, satellite data (Sentinel-2) will be used to identify the study area, then hyperspectral airborne data (HyMap) will be used to refine the area of interest. Subsequently, a snapshot hyperspectral camera will be attached to a UAV to acquire drone-borne data for the investigation of the deposit in more detail. We further argue that the addition of drone-borne hyperspectral data can also vastly improve the accuracy of field mapping in future mineral exploration. Drone-borne measurements can supplement and direct geological observation immediately in the field and therefore allow better integration with in-situ ground investigations. In particular, in inaccessible and remote areas with little infra-structure, such systems are an excellent reconnaissance tool because it allows a systematic, dense and completely non-invasive surveying, which is often not possible using ground-based techniques. Additionally, spectral and spatial information will be integrated by combining drone-borne hyperspectral and Light Detection And Raging (LiDAR) data to provide more accurate classification results.
Ultimately, the corrected drone-borne data provide information on the spectral signatures of outcropping lithologies to the exploration teams. This is achieved by using end-member modelling and classification techniques such as non-linear machine learning algorithms, e.g., Neural Networks and decision tree based methods. The drone based data are integrated in a comprehensive workflow including in-situ acquisitions and results in an hypercloud. The validation of the resulting digital outcrop is performed via field spectroscopy, portable XRF and representative geochemical whole-rock analysis.
The area of interest for this study is the massive carbonatite intrusion at Marinkas Quellen, Namibia. The location is in a remote environment and characterized by difficult terrains and a complete carbonatite suite (e.g. calsio-, ferro- and magnesio-carbonatites). The first two factors would normally impede or restrict traditional field surveying. Preliminary results indicate that drone-borne surveying has a very high potential to directly detect REE-concentrations and indicator minerals for Nb and Ta, in fundamentally lowering the acquisition costs and increasing the information potential of data captured in the field.

Keywords: REEs; Multis-source; Hyperspectral; Exploration; Marinkas Quellen

  • Poster
    WHISPERS - Hyperspectral Image and Signal Processing Workshop, 23.-26.09.2018, Amsterdam, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-28552
Publ.-Id: 28552


Experimental study of the natural convection heat transfer performance for finned oval tubes at different tube tilt angles

Unger, S.; Beyer, M.; Thiele, J.; Hampel, U.

The natural convection heat transfer of finned oval tubes was studied for different tube tilt angles (0° to 40°), fin spacing (6 mm to 16 mm) and Rayleigh numbers (11000 to 130000). Fin efficiency was determined by temperature measurements along the fin surface and temperature gradient calculations. Nusselt number and volumetric heat flux density were chosen as assessment parameters for the thermal performance. A comparison of the experimental data with correlations from literature was made and good agreement was found. Furthermore, the uncertainty by the measurements was evaluated. In the horizontal tube orientation (0°) the Nusselt number increases with fin spacing, however the fin efficiency and the volumetric heat flux density reduce. The tilt angle of the longitudinal tube axis was found to have an essential impact on the thermal performance, in particular when the fin spacing is high. For the higher fin spacing values the horizontal orientation gives highest Nusselt number and volumetric heat flux density. At tube tilt angle of 40° the thermal performance becomes lowest for all fin spacing values. When the fin spacing is low, the effect of tube tilt angle is minor. From the experimental results correlations between Nusselt number, Rayleigh number, fin spacing and tube tilt angle are proposed to assist the future design of heat exchanger with tilted finned oval tubes.

Keywords: Finned oval tubes; Natural convection; Heat transfer; Tube tilt angle; Heat transfer correlation

Permalink: https://www.hzdr.de/publications/Publ-28551
Publ.-Id: 28551


Stoffkreislauf der Metalle – von der Gewinnung bis zum Recycling

Reuter, M. A.; Stelter, M.

In der heutigen Zeit bestimmen Metalle unser tägliches Leben. Im Bereich der Mobilität – sei es beim Auto mit Verbrennungsmotor oder bei Elektrofahrzeugen – sind immer Metalle die wesentlichen Bestandteile, ohne die unsere Welt nicht funktionieren würde. Im Bereich der Kommunikation, der Unterhaltungselektronik, aber auch in der Medizin sind sie ebenfalls unverzichtbar. Ihre herausragenden Eigenschaften – wie Härte, Duktilität, Umformbarkeit, Korrosionsbeständigkeit – machen sie zu idealen Werkstoffen für fast alle Anwendungen. Besonders zeichnet sie aber die Recyclingfähigkeit aus, denn Metalle können prinzipiell zu 100 % nach ihrer Nutzung zurückgewonnen werden.
Dass wir dies bisher nur eingeschränkt tun, hat verschiedene Ursachen. In der Arbeitsgruppe sollen die Aspekte der Kreislaufwirtschaft beleuchtet werden. So werden technologische Möglichkeiten und Grenzen in Beziehung zu den ökonomischen Bezügen gestellt. Gibt es eine optimale Kreislaufführung und, wenn ja, wie sieht sie aus? Welche Faktoren beeinflussen die dafür notwendigen unangewandten Prozesse? Ist es sinnvoll, in jedem Fall zu versuchen, eine Recyclingrate von 100 % zu erreichen? Und ist dies überhaupt möglich?
Eine differenzierte Betrachtung bezüglich unterschiedlicher Stoffgruppen ist dabei erforderlich. Eine weiter in die Details eindringende Betrachtung soll am Beispiel der Metalle den Teilnehmenden der Arbeitsgruppe Chancen und Risiken der Stoffkreislaufführung vermitteln. In Gesprächsrunden und Diskussionen sollen die Vor- und Nachteile von technologischen Prozessen herausgearbeitet und deren Nutzen für die Kreislaufführung der Werkstoffe bewertet werden.

Keywords: Recyclingfähigkeit; Metalle; optimale Kreislaufführung

  • Lecture (others)
    Workshop - Sommerakademie der Studienstiftung, 19.-30.08.2018, St. Johann, Italien

Permalink: https://www.hzdr.de/publications/Publ-28550
Publ.-Id: 28550


Circular Economy engineering - Recycling 4.0 - Challenges of the circular economy

Reuter, M. A.

The last hundred years have brought an unprecedented increase in natural resource use. This trend is likely to continue in the coming decades. Global resource use is expected to double by 2030. For Europe, these developments raise major concerns . Europe's economy depends on an uninterrupted flow of natural resources , metals, minerals, energy carriers and other raw materials , with imports providing a substantial proportion of these materials in many cases. Increasingly, this dependence will be a source of vulnerability, as growing global competition for natural resources has contributed to marked increases in price levels and volatility. Uncertain and unstable prices disrupt the industrial sectors that are dependent on these resources. At the same time, rapid increases in extraction and exploitation of natural resources are having a wide range of negative environmental impacts, particularly in Europe. Air, water and soil pollution, acidification of ecosystems, biodiversity loss, climate change and waste generation put economic and social well-being at risk. Creating a circular economy in Europe can help to address many of these challenges, and further improve the efficiency of resource use. It will have obvious economic benefits, reducing costs and risks while enhancing competitiveness. European leadership in the transition to a circular economy also offers opportunities securing first-mover advantages in the global economy.

The conference will address the issues impacting the transition from the linear take-make-consume-dispose economic model that currently dominates to a circular model that represents a fundamental alternative and explore the huge challenges and business opportunities in a circular economy. The conference will include presentations and panel discussions featuring renowned researchers within circular economy and leading Polish businesses presenting relevant projects and views on why and how the circular economy is introduced in their factories. It will bring together industry leaders, authorities and city planners, technology providers, business consultants, researchers and inventors, all with the common goal of driving innovation in new materials and better, more economic products and services and securing first-mover advantages in the global economy.

Recycling 4.0: digitalizing the system
Recycling 4.0: physics of separation
Recycling 4.0: industrial applications
Recycling 4.0 digital platforms

Keywords: Recycling 4.0

  • Invited lecture (Conferences)
    European Technology Forum 2018 / From Waste to Resources, 26.-27.09.2018, Katowice, Polen
  • Invited lecture (Conferences)
    THM-Kolloquim, 08.10.2018, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28549
Publ.-Id: 28549


SOCRATES 3nd Network-Wide Event

Reuter, M. A.

What have we done so far?
Current Status of SOCRATES projects
Communication, Dissemination and Exploitation progress
What are we going to do? Our contribution to SOCRATES

Keywords: SOCRATES; Copper production process; HSC Sim

  • Lecture (others)
    SOCRATES 3nd Network-Wide Event, 13.-16.02.2018, Bonn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28548
Publ.-Id: 28548


Numerical Studies of Normal Conducting Deflecting Cavity Designs for the ELBE Accelerator

Hallilingaiah, T. G.; van Rienen, U.; Arnold, A.; Lehnert, U.; Michel, P.

Currently, in the electron linac ELBE there is a single beam line. Therefore, at any given time only single user can use the beam. Moreover, as different user experiments require distinct beam intensity settings, not all the experiments fully utilize the 13 MHz CW beam capability of the facility. To utilize the full beam capacity, multiple beam lines can be established by using an array of transverse deflecting structures. For that, an RF cavity was the design choice due to its inherent advantages with respect to repeatability of the kick voltage amplitude and phase, and the possibility of CW operation in the MHz range. Potential design candidates are the CEBAF RF separator, the three proposed crab cavities for the HL-LHC upgrade project, and a novel NC deflecting cavity design. In this comparative study, the figures of merit of the cavities are computed from electromagnetic field simulations for a transverse voltage of 300 kV. This comparative study supported our selection of the deflecting cavity design for ELBE.

Keywords: normal conducting; RF cavity; RF kicker; beam spreader

  • Open Access Logo Contribution to proceedings
    9th International Particle Accelerator Conference, 29.04.-04.05.2018, Vancouver, British Columbia,, Canada
    Proceedings of the 9th International Particle Accelerator Conference: JACoW, ISBN 978-3-95450-184-7, 3824-3827
    DOI: 10.18429/JACoW-IPAC2018-THPAL074

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-28547
Publ.-Id: 28547


Sub-threshold production of K0s mesons and Λ hyperons in Au(1.23A GeV)+Au

Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, L.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Selyuzhenkov, I.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.; Leifels, Y.

We present first data on sub-threshold production of K0s mesons and Λ hyperons in Au+Au collisions at √sNN = 2.4 GeV. We observe an universal scaling of hadrons containing strangeness, independent of their corresponding production thresholds. Comparing the yields, their part> scaling, and the shapes of the rapidity and the pt spectra to state-of-the-art transport model (UrQMD, HSD, IQMD) predictions, we find that none of the latter can simultaneously describe all observables with reasonable χ2 values.

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Permalink: https://www.hzdr.de/publications/Publ-28546
Publ.-Id: 28546


Mixed-valent neptunium oligomer complexes based on cation-cation interactions

Schöne, S.; März, J.; Stumpf, T.; Ikeda-Ohno, A.

Mixed-valent tri- and tetranuclear complexes of neptunium, [{NpIVCl4}{NpVO2Cl(THF)3}2]·THF and [{NpIVCl3}{NpVO2(μ2-Cl)(THF)2}3{μ3-Cl}] (THF = tetrahydrofuran), were synthesised and characterised. Both the complexes are formed via the cation-cation interactions between the Np(IV) centre and the axial oxygens of the neptunyl(V) unit (i.e. transdioxo NpO2+ cation), demonstrating the potential of cation-cation interactions for further exploring the oligomer/cluster chemistry of actinides.

Keywords: actinides; neptunium; mixed-valence; oligomers; polymers; coordination; structure characterisation; cation-cation interactions

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Permalink: https://www.hzdr.de/publications/Publ-28545
Publ.-Id: 28545


Strong absorption of hadrons with hidden and open strangeness in nuclear matter

Adamczewski-Musch, J.; Arnold, O.; Atomssa, E. T.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Chernenko, S.; Chlad, L.; Chudoba, P.; Ciepal, I.; Deveaux, C.; Dittert, D.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kornas, F.; Kotte, R.; Kubos, J.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Linev, S.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Malige, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Mikhaylov, V.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowsk, K.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Prozorov, A. P.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schmidt-Sommerfeld, K.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Siebenson, J.; Silva, L.; Smyrski, J.; Spataro, S.; Spies, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Ungethüm, C.; Vazquez Doce, O.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.

We present the first observation of K- and φabsorption within nuclear matter by means of π- -induced reactions on C and W targets at an incident beam momentum of 1.7 GeV/c studied with HADES at SIS18/GSI. The double ratio (K-/K+)W / (K-/K+)C is found to be 0.319 \pm 0.009(stat)+0.014-0.012 (syst) indicating a larger absorption of K- in heavier targets as compared to lighter ones. The measured φ/K- ratios in π-+C and π^- +W reactions within the HADES acceptance are found to be equal to 0.55±0.03(stat)+0.06−0.07 (syst) and to 0.63±0.05(stat)−0.11+0.11 (syst), respectively. The similar ratios measured in the two different reactions demonstrate for the first time experimentally that the dynamics of the φmeson in nuclear medium is strongly coupled to the K- dynamics. The large difference in the φ production off C and W nuclei is discussed in terms of a strong \phiN in-medium coupling.

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Permalink: https://www.hzdr.de/publications/Publ-28544
Publ.-Id: 28544


Observation of multiple magnetic phases and complex nanostructures in Co implanted amorphous carbon films

Suschke, K.; Gupta, P.; Williams, G. V. M.; Hübner, R.; Markwitz, A.; Kennedy, J.

Room temperature implantation of 30 keV Co ions into an amorphous carbon film with a high fluence of 1.2×1017 Co/cm2 results in formation of magnetic nanostructures displaying multiple magnetic phases. Cross-sectional TEM images show formation of Co containing nanoparticles at the surface and near-surface regions of the implanted films. EDXS measurements suggest the nanoparticles to be composed primarily of Co and O at the surface and Co and C in deeper regions. These nanoparticles with differing compositions were observed to be segregated by a thin layer devoid of Co. Magnetic measurements reveal the presence of superparamagnetic behavior from small CoxC nanoclusters with a blocking temperature of 5 K. There is a small fraction of larger CoxC nanoclusters that show magnetic hysteresis even at room temperature. The saturation magnetic moment is as high as 0.51 μB/Co at 2 K and 0.32 μB/Co at room temperature. Spin-disorder is seen with a range of spin glass temperatures below ∼70 K. Our high fluence Co implantation into amorphous carbon has resulted in the formation of complex magnetic nanostructures composed of cobalt, oxygen, and carbon. These nanostructures give rise to multiple magnetic phases such as superparamagnetism, spin glass, ferromagnetism, and possibly antiferromagnetism.

Keywords: a-C; DLC; Ion implantation; Superparamagnetic; Magnetization; Cobalt oxide; Cobalt carbide

  • Journal of Physics and Chemistry of Solids 127(2019), 158-163

Permalink: https://www.hzdr.de/publications/Publ-28543
Publ.-Id: 28543


On a spectral problem in magnetohydrodynamics and its relevance for the geodynamo

Stefani, F.; Tretter, C.

One of the most remarkable features of the geodynamo is the irregular occurrence of magnetic field reversals. Starting with the operator theoretical treatment of a non-selfadjoint dynamo operator, we elaborate a dynamical picture of those reversals which relies on the existence of exceptional spectral points.

Keywords: geodynamo; magnetohydrodynamics

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Permalink: https://www.hzdr.de/publications/Publ-28542
Publ.-Id: 28542


Laser Plasma Based Accelerators for Radiobiological Applications - From Research Field MATTER to HEALTH

Metzkes-Ng, J.; Levy, Dan

Laser Plasma Based Accelerators for Radiobiological Applications - From Research Field MATTER to HEALTH

  • Invited lecture (Conferences)
    Festive Symposium on the occasion of the inaugruation of the Helmholtz Tel Aviv Office, 22.10.2018, Tel Aviv, Israel

Permalink: https://www.hzdr.de/publications/Publ-28541
Publ.-Id: 28541


Response of the QED(2) Vacuum to a Quench: Long-term Oscillations of the Electric Field and the Pair Creation Rate

Otto, A.; Graeveling, D.; Kämpfer, B.

We consider -- within QED(2) -- the backreaction to the Schwinger pair creation in a time dependent, spatially homogeneous electric field. Our focus is the depletion of the external field as a quench and the subsequent long-term evolution of the resulting electric field. Our numerical solutions of the self consistent, fully backreacted dynamical equations exhibit a self-sustaining oscillation of both the electric field and the pair number depending on the coupling strength.

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Permalink: https://www.hzdr.de/publications/Publ-28540
Publ.-Id: 28540


Probing Interlayer Excitons in a Vertical van der Waals p-n Junction using Scanning Probe Microscopy Technique

Rahaman, M.; Wagner, C.; Mukherjee, A.; Lopez-Rivera, A.; Gemming, S.; Zahn, D. R. T.

Two dimensional (2D) semiconductors feature exceptional optoelectronic properties controlled by strong confinement in one dimension. In this contribution, we studied interlayer excitons in a vertical p-n junction made of bilayer n-type MoS2 and few layers p-type GaSe using current sensing atomic force microscopy (CSAFM). The p-n interface is prepared by mechanical exfoliation onto highly ordered pyrolytic graphite (HOPG). Thus the heterostructure creates an ideal layered system with HOPG serving as the bottom contact for the electrical characterization. Home-built Au tips are used as the top contact in CSAFM mode. During the basic diode characterization, the p-n interface shows strong rectification behavior with a rectification ratio of 104 at ±1 V. The I-V characteristics reveal pronounced photovoltaic effects with a fill factor of 0.55 by excitation below the band gap. This phenomenon can be explained by means of the dissociation of interlayer excitons at the interface. The possibility of the interlayer exciton formation is indicated by density functional theory (DFT) calculations on this heterostructure: the valence band of GaSe and the conduction band of MoS2 contribute to an excitonic state at an energy of about 1.5 eV. The proof of such excitonic transition is provided by photoluminescence measurement at the p-n interface. Finally, photocurrent mapping at the interface under 785 nm excitation provides evidence of efficient extraction of such excitons. Our results demonstrate two dimensional device for future optoelectronics and light harvesting assisted by interlayer excitons in van der Waals heterostructure.

Keywords: van der Waals heterojunction; interlayer exciton; MoS2; GaSe; p-n junction; optoelectronics; density functional theory

Permalink: https://www.hzdr.de/publications/Publ-28539
Publ.-Id: 28539


Damage formation and Er structural incorporation in m-plane and a-plane ZnO

Macková, A.; Malinský, P.; Jagerová, A.; Mikšová, R.; Nekvindová, P.; Cajzl, J.; Rinkevičiūtė, E.; Akhmadaliev, S.

The various crystallographic orientations in semiconductors as ZnO exhibit different resistivity under the ion beam irradiation/implantation. Study of the various crystallographic orientations is mandatory for nano-structured semiconductor system development. This paper reports on the implantation damage build-up, structural modification and Er dopant position in a-plane and m-plane ZnO implanted with Er+ 400 keV ions at the ion fluences 5 × 1014, 2.5 × 1015, 5 × 1015 cm-2 and subsequently annealed at 600 °C in O2 atmosphere using Rutherford Back-Scattering spectrometry (RBS) in channelling mode as well as using Raman spectroscopy. Strongly suppressed surface damage formation was observed in both crystallographic orientations compared to the deep damage growth with the increased ion implantation fluence. More progressive damage accumulation appeared in m-plane ZnO compared to a-plane ZnO. Simultaneously, the strong Er out-diffusion depth profile in m-plane ZnO accompanied by the damage accumulation at the surface was observed after the annealing. Contrary, the surface recovery accompanied by Er concentration depth profiles keeping a normal distribution with a small maximum shift to the surface was observed in a-plane ZnO. Different structure recovery and Er behaviour was evidenced in a-plane and m-plane ZnO by RBS-C, moreover Raman spectroscopy proved a lower damage at higher ion fluences introduced in a-plane ZnO compared to m-plane. The structure modifications were discussed in connection with a damage accumulation and Er concentration depth profile shape in various ZnO crystallographic orientations in as-implanted and as-annealed samples.

Keywords: a-Plane and m-plane ZnO doped; Damage accumulation asymmetry; Er ion implantation in ZnO; RBS channelling; Damage depth profiling

Permalink: https://www.hzdr.de/publications/Publ-28538
Publ.-Id: 28538


Defects in hydrogen implanted SiC

Zhang, X.; Li, Q.; Wang, M.; Zhang, Z.; Akhmadaliev, S.; Zhou, S.; Wu, Y.; Guo, B.

SiC is a widely used wide-bandgap semiconductor. Ion implantation is often employed in SiC for doping, defect engineering and transferring of SiC thin films on different substrates. To transfer SiC or to get freestanding thin SiC films by "smart-cut" [Appl. Phys. Lett. 112 (2018) 192102], a large fluence of hydrogen (proton) ion implantation will be applied. Here, we show the structure and defect properties in 6H-SiC single crystals after hydrogen implantation up to a fluence of 5 x 1016 cm-2 at different energies of ions. We present the characterization by Rutherford Backscattering/Channeling spectrometry, Raman spectroscopy and electron spin resonance. Upon H+ ion implantation, point defects are mainly created and cause the lattice vibration softening. Our analysis also suggests that H+ ion implantation induces less lattice disorder than heavy ions at fluences producing the same number of displacements per atom. We also discuss the possible nature of the point defects and their influence on the electrical properties.

Keywords: SiC; Defects; Ion implantation; Raman-Spectroscopy; Damage formation; Ion; Surface; Neutron

Permalink: https://www.hzdr.de/publications/Publ-28537
Publ.-Id: 28537


Thermocapillary convection during hydrogen evolution at microelectrodes

Massing, J.; Mutschke, G.; Baczyzmalski, D.; Hossain, S. S.; Yang, X.; Eckert, K.; Cierpka, C.

The origin of strong electrolyte flow during water electrolysis is investigated, that arises at the interface between electrolyte and hydrogen bubbles evolving at microelectrodes. This Marangoni convection was unveiled only recently (Yang et al., PCCP, 2018, [1]) and is supposed to be driven by shear stress at the gas-liquid interface caused by thermal and concentration gradients. The present work firstly allows a quantification of the thermocapillary effect and discusses further contributions to the Marangoni convection which may arise also from the electrocapillary effect. Hydrogen gas bubbles were electrolytically generated at a horizontal Pt microelectrode in a 1MH2SO4 solution. Simultaneous measurements of the velocity and the temperature field of the electrolyte close to the bubble interface were performed by means of particle tracking velocimetry and luminescent lifetime imaging. Additionally, corresponding numerical simulations of the temperature distribution in the cell and the electrolyte flow resulting from thermocapillary stress only were performed. The results confirm significant Ohmic heating near the micro-electrode and a strong flow driven along the interface away from the microelectrode. The results further show an excellent match between simulation and experiment for both the velocity and the temperature field within the wedge-like electrolyte volume at the bubble foot close to the electrode, thus indicating the thermocapillary effect as the major driving mechanism of the convection. Further away from the microelectrode, but still below the bubble equator, however, quantitative differences between experiment and simulation appear in the velocity field, whereas the temperature gradient still matches well. Thus, additional effects must act on the interface, which are not yet included in the present simulation. The detailed discussion tends to rule out solution-based effects, generally referred to as solutal effects, whereas electrocapillary effects are likely to play a role. Finally, the thermocapillary effect is found to exert a force on the bubble which is retarding its departure from the electrode.

Keywords: Water electrolysis; Thermocapillary convection; Microbubbles; Fluorescence lifetime imaging; Numerical simulation; Hydrogen evolution

  • Open Access Logo Electrochimica Acta 297(2019), 929-940
    DOI: 10.1016/j.electacta.2018.11.187
  • Lecture (Conference)
    8-th International Symposium on Bifurcations and Instabilities in Fluid Dynamics, 16.-19.07.2019, Limerick, Irland

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Permalink: https://www.hzdr.de/publications/Publ-28536
Publ.-Id: 28536


Messung der Marangoniströmung an elektrochemisch erzeugten Wasserstoffblasen

Massing, J.; Baczyzmalski, D.; Yang, X.; Mutschke, G.; Eckert, K.; Cierpka, C.

Bei der Wasserstoffelektrolyse kann es aufgrund von Gradienten in der Konzentration und der Temperatur zu Gradienten in der Oberflächenspannung an der Phasengrenzfläche der Wasserstoffblase kommen. Die dadurch angetriebene Marangoniströmung konnte erstmals an einer Mikroelektrode für verschiedene Potentiale gemessen werden. Die Strömungsgeschwindigkeit korreliert eindeutig mit dem elektrischen Strom. Für die vorgestellte Untersuchung werden sowohl der Einfluss des Konzentrationsgradienten als auch der Einfluss des Temperaturgradienten diskutiert und eine Größenordnungsabschätzung zur Beschreibung des Phänomens durchgeführt. Erste Ergebnisse zu Temperaturmessungen auf der Basis von temperatursensitiven Partikeln an der Wasserstoffblase ergänzen die in der Größenordnungsabschätzung gemachten Annahmen und zeigen die lokale Erwärmung am Blasenfuß.

Keywords: Elektrolyse; Gasentwicklung; Wasserstoff; Mikroelektrode; PIV; Temperaturmessung

  • Lecture (Conference)
    26. Fachtagung "Experimentelle Strömungsmechanik", 04.-06.09.2018, Rostock, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28535
Publ.-Id: 28535


Longitudinal modulation of electron-cooled C-12(6+) and O-16(8+) ion beams at heavy ion storage ring CSRe

Wang, H.; Wen, W.; Huang, Z.; Zhang, D.; Hai, B.; Bussmann, M.; Winters, D.; Zhao, D.; Zhu, X.; Li, J.; Li, X.; Mao, L.; Mao, R.; Zhao, T.; Yin, D.; Wu, J.; Yang, J.; Yuan, Y.; Ma, X.

The longitudinal dynamics of electron-cooled and radio-frequency (RF)-bunched C-12(6+) and O-16(8+) ion beams have been investigated at a heavy-ion experimental cooler storage ring CSRe. An rf-buncher was employed to longitudinally modulate the ion beams. A new resonant Schottky pick-up was applied to monitor the intensities and longitudinal dynamics of stored and electron-cooled ion beams. Using electron-cooling, the separated Schottky noise signals of the C-12(6+) and O-16(8+) ions were clearly observed in the Schottky spectrum. The storage times and the particle numbers of both ion beams were measured by Schottky noise, which demonstrated the ability to perform Schottky mass spectrometry measurements and also the measurement of highly charged ions at the CSRe. In addition, an enhancement of the Schottky noise signals was observed for rf-bunched ion beams, which could be used to diagnose the intensity ion beams at storage rings. Finally, a broadly longitudinal manipulation of the ion beams by scanning the bunching frequency was realized. The investigation of electron-ion recombination experiment at ultra-low collision energies by scanning the bunching frequency of the ion beams at the storage ring CSRe is proposed.

Keywords: electron cooloing; schottky; ion beam

Permalink: https://www.hzdr.de/publications/Publ-28534
Publ.-Id: 28534


Coatings in harsh space environment

Pelizzo, M. G.; Corso, A. J.; Tessarolo, E.; Böttger, R.; Hübner, R.

In recent years, the study of space agent effects on optical coatings has become priority in view of future selected missions which will explore increasingly hostile environments. The impact on the morphology, on the structure and on the performance of coatings and materials due to ion and electron irradiation has been studied through various investigative techniques [1,2]. The irradiation sessions have been carried out at accelerators adopting different experimental regimes to reproduce space conditions in laboratory. A predictive model of the optical performance based on of the damage induced by protons and alpha particles has been developed [3]. Changes in the reflectance and transmittance properties have been attributed to density and refraction index variations due to implantation of low energetic particles. Bubble formation has been observed in metals, while delamination occurs when particles accumulated at interfaces, such as those in metal-protected thin films. Blistering of top layers has been observed in oxide-protected metal coatings (Fig.1). Impact on the performance of the coatings in various spectral ranges including extreme ultraviolet is discussed.
[1] Pelizzo, M.; Corso, A.J.; Zuppella, P.; Windt, D.L.; Mattei, G.; Nicolosi P., Stability of extreme ultraviolet multilayer coatings to low energy proton bombardment. Opt. Express 2011, 19, 14838-14844.
[2] Zuccon, S.; Napolitani, E.; Tessarolo, E.; Zuppella, P.; Corso, A.J.; Gerlin, F.; Nardello, M.; Pelizzo, M.G. Effects of helium ion bombardment on metallic gold and iridium thin films. Opt. Mat. Express 2015, 5(1), 176–187.
[3] M.G. Pelizzo, A.J. Corso1, E. Tessarolo, R. Böttger, R. Hübner, E. Napolitani, M. Bazzan, M. Rancan, L. Armelao, W. Jark, D. Eichert, A. Martucci, Morphological and functional modifications of optical thin films for space applications irradiated with low-energy helium ions, paper in preparation, 2018.

  • Lecture (Conference)
    Physics of X-Ray and Neutron Multilayer Structures, PXRNMS 2018, 07.-09.11.2018, Palaiseau, France

Permalink: https://www.hzdr.de/publications/Publ-28533
Publ.-Id: 28533


Effect of Ni-Ion Implantation into TiO2 Thin Films for Improving Resistive Switching Properties

Das, D.; Barman, A.; Bhowmick, S.; Phase, D. M.; Rajput, P.; Jha, S. N.; Kanjilal, D.; Hübner, R.; Kanjilal, A.

The expedition for non-volatile memories (NVM) is still on, owing to the rapid convergence of current memory technologies to their physical limits [1]. In recent years, TiO2 thin film-based Resistive Random Access Memory (RRAM) devices have shown great promise to the future NVM technology due to their low cost, easy fabrication, scalability, and higher operation speed [1-2]. Switching from a low-resistance state (LRS) to the high-resistance state (HRS) is quite debatable [2]. However recent studies [3-4] suggest controlled defect (oxygen vacancy, OV) engineering by ion implantation may significantly improve the switching performance. In this respect, controlled incorporation of foreign elements in the host (TiO2 films) by ion beam implantation would be advantageous for OV formation.Results obtained for 35 keV Ni-doped TiO2 thin films will be presented here, emphasizing the enhancement of the LRS to HRS ratio for improving the resistive switching properties. The formation of graded Ni layer, regions will be addressed by detailed transmission electron microscopy studies. Whereas the extended X-ray absorption fine structure (EXAFS) measurements will show an increase in white light intensity at the Ni-K edge along with the change in pre-edge feature (compared to metallic Ni), indicating the interaction of Ni ions with the host matrix. Further, Ni-doping induced evolution of Ti3+ state will be demonstrated by X-ray photo electron spectroscopy, supporting the development of OV. Following the fabrication of Au/Ni-TiO2/Pt RRAM devices, charge transport mechanism will finally be explained on the basis of different conduction mechanisms.
[1] Yang, J. J., Pickett, M. D., Li, X., Ohlberg, D. A., Stewart, D. R., & Williams, R. S. (2008) , Nature Nanotech. 3(7), 429.
[2] Lee, M. H., Kim, K. M., Kim, G. H., Seok, J. Y., Song, S. J., Yoon, J. H., & Hwang, C. S. (2010), Applied Physics Letters, 96(15), 152909.
[3] Pan, X., Shuai, Y., Wu, C., Luo, W., Sun, X., Zeng, H & Zhang, W. (2016), Applied Physics Letters, 108(3), 032904.
[4] Wylezich, H., Mähne, H., Heinrich, A., Slesazeck, S., Rensberg, J., Ronning & Mikolajick, T. (2015). Journal of Vacuum Science & Technology B, 33(1), 01A105.

  • Poster
    5th International Conference on Ion Beams in Materials Engineering and Characterizations, IBMEC 2018, 09.-12.10.2018, New Delhi, India

Permalink: https://www.hzdr.de/publications/Publ-28532
Publ.-Id: 28532


Developing nanocrystalline thin film based radiation dosimeter

Pal, S.; Bhowmick, S.; Das, D.; Khan, S. A.; Kanjilal, D.; Hübner, R.; Kanjilal, A.

Radiation dosimetry is an important field of research due to its potential in various applications like food safety, personal dosimetry, environmental monitoring, radiation therapy, etc [1]. In general, most radiation dosimetric studies are related with electromagnetic radiation (γ radiation, UV radiation, etc.). However, the increased use of hadron therapy (radiation therapy using charged particles) in cancer and tumor treatment demands inclusion of ion beam dosimetry study for radiation dosimetry [2]. In this regard, it is a need to develop novel dosimeters with thin films for online monitoring of the radiation dose delivered to patient. In contrast to powder sample based dosimeter, here very less material will be required demanding very high sensitive phosphors. Aluminium oxide (Al2O3) (specially, carbon doped) can be a good choice due to its very high thermoluminescence (TL) sensitivity [2]. Moreover, this material is considered to be the best material for optically stimulated luminescence (OSL), a suitable radiation dosimetric technique for online monitoring. Regarding thin films, choice of substrate is always a matter of interest. Here, a comprehensive radiation dosimetric study of as-grown and annealed Al2O3 deposited on different substrates (i.e. silicon, Al foil, kapton tape, etc) by using RF magnetron sputtering and anodized porous Al2O3 will be presented. The variation in radiation response will be discussed in the light of detailed structural and optical properties analysis of the said thin films [3].
1. Thermoluminescence of solids, SWS Mckeever, Cambridge university press, 1988.
2. G. O. Sawakuchi et al. J. Appl. Phys. 104 (2008) 124903.
3. W. L. Xu et al. Appl. Phys. Lett. 85 (2004) 4364.

  • Lecture (Conference)
    International Conference on Current Trends in Materials Science and Engineering, CTMSE 2018, 19.-20.01.2018, Kolkata, India

Permalink: https://www.hzdr.de/publications/Publ-28531
Publ.-Id: 28531


Study of thermoluminescence property of C+ ion doped anodized alumina

Bhowmick, S.; Das, D.; Asirvatham, J.; Khan, S. A.; Sen, D.; Hübner, R.; Kanjilal, D.; Kanjilal, A.

The application of thermoluminescence (TL) has created immense interest due to their potential to determine radiation doses for food-safety, radiation therapy, personal dosimetry, environmental monitoring, etc. However, the performance of a phosphor relies on thermally stimulated light emission from luminescent centres created during the exposure to an ionizing radiation. Aluminum oxide (Al2O3) is one of the promising materials for dosimetry. Although this material was forgotten for a long time due to its low sensibility compared with that of TLD-100, it recently regained interest owing to the development of anion defects in Al2O3:C single crystals. It was reported to be highly sensitive, even more than TLD-100, though conventional crystal growth technique requires high temperature in the presence of a high tumbling atmosphere. Nevertheless, the TL sensitivity of crystalline Al2O3 can be enhanced by doping with carbon, but this is only good for low dose radiation monitoring (typically 0.1-100 Gy). Interestingly, a prominent TL sensitivity can be achieved from nanocrystals with increasing surface-to-volume ratio because of increasing surface states. Therefore, judicial use of Al2O3 nanocrystallites will give a fertile ground for offline dose monitoring. The nanotrenches of anodized alumina in this respect can also give additional path for improving efficiency, which can be enhanced further by controlled introduction of C in Al2O3 matrix. Since ion beam implantation is known to be a powerful method because of its ability to control over distribution of dopants and residual defects, it is therefore important to understand the impact of C+ ions in controlling the formation of traps in anodized alumina and also to explore its suitability for ion beam dosimetry by following the TL glow curves with increasing fluence (i.e. ions/cm2).
To execute this plan, after optimizing the porosity, the penetration depth of C+ ions in Al2O3 layers have been calculated by SRIM. Typical porous structure in the present set of samples is shown in Figs. 1 and 2. Based on this understanding, the anodized alumina has been exposed to 50 keV C+ ions in the fluence range of 2.33×1015 to 1.3×1016 ions/cm2. Following the initial structural analysis by XRD, TL response of the ion irradiated samples was characterized, showing a systematic rise in intensity with increasing fluence (Figure 3). For understanding of the underlying process, the anodized alumina before and after irradiation have now been studied by various techniques, like SEM, TEM, XRD, RBS, and XPS.

  • Open Access Logo Contribution to external collection
    in: IUAC Annual Report 2016-2017, New Delhi: Inter University Accelerator Centre, 2018, 148-149

Permalink: https://www.hzdr.de/publications/Publ-28530
Publ.-Id: 28530


Understanding the role of carbon in active trap centre formation in porous alumina

Bhowmick, S.; Pal, S.; Das, D.; Khan, S. A.; Gupta, M.; Barman, S. R.; Kanjilal, D.; Hübner, R.; Kanjilal, A.

In recent days, carbon doped alumina (Al2O3:C) are gaining immense interest as a potential radiation dosimetric material due to very high thermoluminescence (TL) sensitivity [1]. Despite of some theoretical predictions [2, 3] as well as experimental results, exact role of carbon in forming active trap centres in alumina matrix is still not conclusive, and thus it requires further investigation. Here we report a detailed study of porous alumina in a systematic way by various complementary techniques, such as HAADF-STEM, EDS mapping, X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) before and after carbon doping. For that, ion beam implantation technique has been employed due to controlled incorporation of carbon in selective areas of Al2O3. Further, the anodized alumina with a porous structure is expected to play a crucial role due to high surface-to-volume ratio. Amorphous porous alumina has been synthesized electrochemically [4] where the porous structure have been confirmed by SEM and TEM. The amorphous nature is also consistent with the GIXRD results. The corresponding elemental mapping suggests the carbon penetration depth in the amorphous Al2O3 matrix. Detailed XAS and depth dependent XPS studies reveal possible role of carbon atoms in Al2O3 as active trap centres, and so the TL response. The observed results are in good agreement with the recent theoretical works, and therefore will be helpful for further improvement of dosimetric sensing.
1. G. O. Sawakuchi et al. J. Appl. Phys. 104 (2008) 124903
2. H. D. Tailor et al. J. Vac. Sci. & Technol. A 33 (2015) 01A120
3. L. Ao et al. J. Appl. Phys. 122 (2017) 025702
4. H. Masuda et al. Science 268 (1995) 1466

  • Poster
    International Conference on Current Trends in Materials Science and Engineering, CTMSE 2018, 19.-20.01.2018, Kolkata, India

Permalink: https://www.hzdr.de/publications/Publ-28529
Publ.-Id: 28529


Carbon Nanotubes – A Route Towards Space Application

Abbe, E.; Renger, T.; Sznajder, M.; Klemmed, B.; Starruß, E.; Hübner, R.; Schüler, T.; Bärtling, Y.; Muchow, B.; Tajmar, M.; Schmiel, T.

Over the last years, Carbon Nanotubes (CNTs) drew interdisciplinary attention. Regarding space technologies, a variety of potential applications were proposed and pre-investigated, e.g. electro-static discharge (ESD) coatings, electromagnetic interference (EMI) shields or high-strength materials for structural applications. However, no complex data regarding the behaviour and degradation process of CNTs under space environment have been collected so far and only a limited number of real space experiments and applications of CNTs exists nowadays. Therefore, it is necessary to investigate the influence on these new materials in space environment and to revaluate the application potential of CNTs in space technologies.
To this end, the Carbon Nanotubes – Resistance Experiment (CiREX) was developed. CiREX is a small and compact experiment, which is designed for small satellites like Cubesats. These satellites are a class of nanosatellites with a standardised size and form. CiREX was developed for SOMP2 (Student Oxygen Measurement Project 2) wich is a double unit Cubesat. The design and construction was performed by master and PhD students at the Technische Univeristät Dresden.
CiREX is the first in-situ space material experiment for CNTs. Multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) show extraordinarily properties. As a result of the nearly one-dimensional structure, the electrical transport is ballistic which only applies within the tubes. In CNT networks, the contacts between the tubes become more effective and therefore electrical resistance increases. Consequently, the ohmic behaviour of CNT networks is strongly influenced by adsorbed ions and molecules, the defect structure, the contact resistance of the network and thermal modifications. The influence of these effects were considered during the design process of CiREX. Accordingly, this experiment measures the electrical resistance of CNT networks under the harsh space environment. Its design, electrical measurement and the satellites interfaces will be discussed in detail.
To evaluate the data obtained from CiREX, ground validation tests are mandatory. As part of a test series the behaviour of CNTs under solar light were examined. SWNTs, MWNTs and multi-walled carbon nanotubes/resin composite (ME) were exposed to a solar light simulator. Furthermore, we have measured the resistance of the samples during the irradiation. After the exposure, the defect density and surface structure of the tubes were investigated with Raman scattering and scanning electron microscope. The results show a clear indication that solar light can influence the electrical behaviour and the tubes structure.

  • Poster
    14th International Symposium on Materials in the Space Environment, ISMSE 14th, 01.-05.10.2018, Biarritz, France

Permalink: https://www.hzdr.de/publications/Publ-28528
Publ.-Id: 28528


Towards anatase promotion in Cr (co-)doped TiO2 sputtered films

Gago, R.; Prucnal, S.; Hübner, R.; Jiménez, I.; Javier Palomares, F.

Many applications of TiO2 partially rely on its good performance as solvent for impurities [1]. In particular, metal (cation) dopants can functionalize or enhance TiO2 as catalyst [2], diluted magnetic semiconductor [3] or transparent conductor [4]. Special attention has been devoted to TiO2 photoactivity where doping has been extensively studied towards band-gap narrowing to achieve visible-light (VISL) response [2]. Metal doping (Cr,Mo,V…) can increase VISL absorption but introduces severe structural distortions that additionally result in carrier recombination centers [4]. Our research seeks for processing routes to improve the structural quality of Cr (co-)doped films produced by magnetron sputtering with emphasis in phase selectivity. Namely, the promotion of anatase is preferred due to the superior photoactivity of this phase or phase mixtures with high anatase content [5]. Recently [6], we have reported the impact of non-contact flash-lamp annealing (FLA) on monolithic TiO2(:Cr) films. By tuning the energy flux, FLA yields customized TiO2 phases but, in doped structures, phase formation only takes place for low Cr contents (< 5 at.%) and the rutile structure is mostly favored. On the contrary, modulated film architecture has shown promising results for anatase growth [7]. In this paper, such scheme, in conjunction with FLA, is explored in detail to optimize the film structural quality and growth design.
REFs: [1] Sacerdoti et al., J. Solid State Chem. 177, 1781 (2004); [2] Henderson, Surf. Sci. Rep. 66, 185 (2011); [3] Matsumoto et al. Science 291, 854 (2001); [4] Serpone et al., J. Phys. Chem. B 110, 24287 (2006); [5] Scanlon et al., Nat. Mater. 12, 798 (2013); [6] R. Gago, S. Prucnal et al., J. Alloys & Compounds 729 (2017) 438; [7] R. Gago, S. Prucnal et al., to be submitted.

Keywords: TiO2; magnetron sputtering; flash-lamp-annealing; photocatalysis

  • Lecture (Conference)
    16th International Conference on Plasma Surface Engineering, PSE 2018, 17.-21.09.2018, Garmisch-Partenkirchen, Germany

Permalink: https://www.hzdr.de/publications/Publ-28527
Publ.-Id: 28527


Unraveling energy loss processes of low energy heavy ions in 2D materials

Wilhelm, R. A.; Grande, P. L.

Structuring of 2D materials and their heterostructures with ion beams is a challenging task, because typically low ion energies are needed to avoid damage to a substrate. In addition, at the very first monolayers of a material, ions are not yet in charge equilibrium, i.e. they may either charge up or neutralize depending on their velocity. The change in electronic structure of the ion during scattering affects the energy, which can be transferred to the recoil and therefore the energy available for defect formation. In order to make reliable use of ion beams for defect engineering of 2D materials, we present here a new model for charge state and charge exchange dependent kinetic energy transfer. Our model can be applied to all ion species, ion charge states, and energies. It is especially powerful for predicting charge state dependent stopping of slow highly charged ions.

Keywords: Ions; Stopping; 2D Materials; Highly Charged Ions

  • Open Access Logo Communications Physics 2(2019)1, 89
    DOI: 10.1038/s42005-019-0188-7
  • Lecture (Conference)
    Frühjahrestagung der Deutschen Physikalischen Gesellschaft, Sektion Festkörperphysik, 31.03.-05.04.2019, Regensburg, Deutschland
  • Poster
    European Conference on Atoms, Molecules, and Photons (ECAMP), 07.-12.04.2019, Florenz, Italien
  • Poster
    Electron, Photon, and Ion Collisions on Molecular & Atomic Nanostructures (EPIC-MAN), 22.07.2019, Caen, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-28526
Publ.-Id: 28526


A radiation response model to assess clinical RBE variability in proton therapy

Eulitz, J.; Lutz, B.; Wohlfahrt, P.; Dutz, A.; Enghardt, W.; Krause, M.; Troost, E. G. C.; Lühr, A.

Currently, the clinical implementation of a variable relative biological effectiveness (RBE) in proton therapy is controversially discussed. First clinical evidence indicated a variable RBE for brain irradiation, which needs to be substantiated. For assessing clinical RBE variability, we established a normal tissue response model and applied it to follow-up magnetic resonance (MR) images.

Four glioma patients (grade II-III) showing late morphological T1-weighted contrast-enhanced (T1w-CE) MR image changes and suspicious necrosis were considered. All were treated with passive scattering at the UniversityProtonTherapyDresden (UPTD). Dose, and linear energy transfer (LET) were calculated with a TOPAS-based Monte-Carlo (MC) simulation framework dosimetrically validated for UPTD. To establish radiation response, logistic regression models based on dose and / or LET were trained on T1w-CE MR voxels classified as change (1) or no change (0). Model performance was assessed by the area under the curve (AUC) performing leave-one-out cross validation.

Correlating image changes with dose and LET resulted in high predictive power (AUC=0.87). TD50 values (dose at which 50% of patient voxels show toxicity) decreased linearly with LET (intercept and slope of 88.9 Gy and -10.9 Gy/(keV/μm), respectively). Models considering either dose or LET performed only moderately (AUC of 0.68 and 0.64, respectively). LET averaging method (dose-averaged or track-averaged) had no impact on model performance.

Only the model based on dose and LET led to high predictive power for late MR image changes, suggesting a variable radiation response and, hence, non-constant RBE. This study enables and encourages in-depth assessment of clinical RBE variability in proton therapy.

Keywords: Proton Therapy; Clinical RBE; Monte-Carlo; Passive Scattering

  • Lecture (Conference)
    58th annual conference of the particle therapy co-operative group (PTCOG), 10.-15.06.2019, Manchester, England

Permalink: https://www.hzdr.de/publications/Publ-28525
Publ.-Id: 28525


From curvilinear magnetism to shapeable magnetoelectronics

Makarov, D.

Extending 2D structures into 3D space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and 3D shape. We study 3D curved magnetic thin films and nanowires where new fundamental effects emerge from the interplay of the geometry of an object and topology of a magnetic sub-system [1,2]. On the other hand, we explore the application potential of these 3D magnetic architectures for the realization of mechanically shapeable magnetoelectronics [3] for automotive but also virtual and augmented reality appliances [4,5]. The balance between the fundamental and applied inputs stimulates even further the development of new theoretical methods and novel fabrication/characterization techniques [6-8].

[1] R. Streubel et al., Magnetism in curved geometries. J. Phys. D: Appl. Phys. (Review) 49, 363001 (2016).
[2] D. Sander et al., The 2017 magnetism roadmap. J. Phys. D: Appl. Phys. (Review) 50, 363001 (2017).
[3] D. Makarov et al., Shapeable Magnetoelectronics. Appl. Phys. Rev. (Review) 3, 011101 (2016).
[4] G. S. Cañón Bermúdez et al., Magnetosensitive e-skins with directional perception for augmented reality. Science Advances 4, eaao2623 (2018).
[5] G. S. Cañón Bermúdez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).
[6] R. Streubel et al., Retrieving spin textures on curved magnetic thin films with full-field soft X-ray microscopies. Nature Communications 6, 7612 (2015).
[7] T. Kosub et al., All-electric access to the magnetic-field-invariant magnetization of antiferromagnets. Phys. Rev. Lett. 115, 097201 (2015).
[8] T. Kosub et al., Purely antiferromagnetic magnetoelectric random access memory. Nature Communications 8, 13985 (2017).

Keywords: magnetic field sensors; flexible electronics; curvature effects in magnetism

  • Invited lecture (Conferences)
    Invited talk at the NC State University, 16.01.2019, Raleigh, USA

Permalink: https://www.hzdr.de/publications/Publ-28524
Publ.-Id: 28524


Simulation challenges for the community in complex LPA designs at the example of hybrid LWFA - PWFA

Debus, A.; Pausch, R.; Steiniger, K.; Garten, M.; Rudat, S.; Hübl, A.; Widera, R.; Couperus Cabadağ, J. P.; Kurz, T.; Schöbel, S.; Köhler, A.; Zarini, O.; Heinemann, T.; de La Ossa, A.; Irman, A.; Schramm, U.; Bussmann, M.

Increasingly complex experimental LPA designs, such as current hybrid LWFA-PWFA experiments integrate different physics regimes (LPA, e- beam tracking, gas dynamics, etc...) require simulations at multiple scales (more physics, more data). Working in mixed teams of experimentalists and theoreticians with specialists from different affiliations requires tighter interfacing of different codes with experimental data analysis.

Key challenges for laser-plasma accelerator simulations are
* Predictive start-to-end simulations, while retaining the ability to understand and optimize sub-systems.
* Common interfacing standards (OpenPMD -- exchange particle and mesh based data from scientific simulations and experiments)
* Tolerance analysis (Analyse the impact of variations in initial conditions and accelerator design).
* Synthetic Diagnostics (Experimental diagnostics modeled in-situ at simulation time)
* Simulation as-a-service (Within some predefined range of simulation scenarios, running additional simulation for some LPA design is made easy for non-specialists.)

Keywords: PIConGPU; synthetic diagnostics; simulation-as-a-service; tolerance analysis; parameter scans; OpenPMD; predictive start-to-end simulations; GUI

  • Lecture (Conference)
    EuPRAXIA Yearly Meeting, 19.-22.11.2018, Frascati, Italy

Permalink: https://www.hzdr.de/publications/Publ-28523
Publ.-Id: 28523


From LWFA bunch durations to bunch profile and micro-structure: Longitudinal electron bunch diagnostics for LWFA based on broadband, spectral CTR measurements at single-shot

Debus, A.; Zarini, O.; Laberge, M.; Couperus Cabadağ, J. P.; Koehler, A.; Kurz, T.; Schoebel, S.; Kraemer, J.; Hannasch, A.; Zgadzaj, R.; Bussmann, M.; Downer, M.; Schramm, U.; Irman, A.

Laser-wakefield accelerators (LWFA) feature electron bunch durations on a scale of a few fs. Precise knowledge of the longitudinal profile of such ultra-short electron bunches is essential for the design of future table-top X-ray light sources. The resolution limit, as well as the limited reproducibility of electron bunches, pose big challenges for LWFA beam diagnostics.

Spectral measurements of broadband transition radiation from LWFA electron bunches passing through a metal foil are especially promising for analyzing ultrashort longitudinal bunch characteristics ranging from of tens of fs down to sub-fs.

Our broadband, single-shot spectrometer combines the TR spectrum in UV/VIS (200-1000nm), NIR (0.9-1.7μm) and mid-IR (1.6-12μm). A complete characterization and calibration of the spectrometer has been done with regard to wavelengths, relative spectral sensitivities and absolute photometric sensitivity. Our spectrometer is able to characterize electron bunches with charges as low as 1 pC and resolve time-scales from 0.7 to 40 fs.

We present results from recent measurement campaign by analyzing transition radiation spectra produced by nC class LWFA electron bunches using ionization-injection, while complementary data on the transverse bunch profile is provided by simultaneously imaging the CTR in the far- and near-field.

We discuss the data analysis from detection to profile reconstruction with error analysis and show electron bunch profiles as determined from experimental density scan measurements.

Keywords: broadband spectrometer; single-shot bunch length measurement; coherent transition radiation; absolute calibration; electron bunch duration; longitudinal profile; absolute calibration; UV; VIS; NIR; MIR

  • Lecture (Conference)
    Advanced Accelerator Concepts (AAC 2018), 12.-17.8.2018, Breckenridge, Colorado, United States

Permalink: https://www.hzdr.de/publications/Publ-28522
Publ.-Id: 28522


Traveling-Wave Electron Acceleration: Laser-plasma acceleration without limits from dephasing and pump-depletion

Debus, A.; Pausch, R.; Huebl, A.; Steiniger, K.; Widera, R.; Cowan, T.; Schramm, U.; Bussmann, M.

We show how to simultaneously eliminate both dephasing and depletion constraints of laser-plasma accelerators. For this we introduce the Traveling-wave electron accelerator (TWEAC) approach, in which the wakefield driver is not provided by a single laser pulse, but instead by a region of overlap of two obliquely incident, ultrashort laser pulses with tilted pulse-fronts in the line foci of two cylindrical mirrors, aligned to coincide with the trajectory of subsequently accelerated electrons. Such a geometry of laterally coupling the laser into a plasma allows for the region of overlap to move with the vacuum speed of light, while its field is continuously being replenished by the successive parts of the laser pulse. Supported by 3D particle-in-cell simulations, we show that this results in quasi-stationary acceleration conditions for an electron bunch along the total acceleration length, which allows to break both the dephasing and depletion limit of LWFA.

Particularly, and in contrast to LWFA and PWFA, a single TWEAC-stage can arbitrarily be extended in length to higher electron energies without changing the underlying acceleration mechanism. Additionally, the TWEAC geometry greatly facilitates reducing beam transport distances between the laser-plasma accelerator and subsequent insertion devices, such as undulators, plasma lenses or colliding laser pulses, to below millimeters. After analyzing stability of acceleration and possible limits of the scheme, we present energy scaling laws for both laser as well as electrons and detail experimental design considerations.

In the future, we expect the new TWEAC technique to greatly reduce the need for staging in order to attain higher electron energies beyond 10GeV, possibly reaching for the energy frontier of high-energy physics. For lower GeV-scale electron energies, TWEAC at high plasma densities and 10TW-class laser systems could enable compact accelerators at kHz-repetition rates.

Keywords: Laser-produced plasmas; Plasma-based accelerators; Laser-wakefield acceleration; Traveling-wave electron acceleration; TWEAC

  • Lecture (Conference)
    Advanced Accelerator Concepts 2018 (AAC 2018), 12.-17.8.2018, Breckenridge, Colorado, United States

Permalink: https://www.hzdr.de/publications/Publ-28521
Publ.-Id: 28521


Advancing predictive capabilties of LWFA simulations using PIConGPU: From improved modeling to novel measurement methods via synthetic radiation diagnostics

Debus, A.; Pausch, R.; Steiniger, K.; Widera, R.; Huebl, A.; Garten, M.; Irman, A.; Couperus Cabadağ, J.; Zarini, O.; Koehler, A.; Schramm, U.; Bussmann, M.

In a close interplay between particle-in-cell simulations and experimental measurements, we present new insights into the modeling of laser wakefield accelerators and discuss the arising challenges for laboratory diagnostics. These challenges were tackled by developing new methods for determining key parameters of the experiment by studying synthetic radiation diagnostics predicted by simulations.

The combination of an unprecedented experimental campaign studying the parameter dependence of beam loading during LWFA and an accompanying, extensive simulation campaign using the 3D3V particle-in-cell code PIConGPU made it possible to provide unique feedback between experiment and theory. This poster shows the step-by-step improvements through this interplay from the simulation perspective. Quantitatively more accurate methods such as the use of Gauss-Laguerre modes or a variety of ionization models are presented as well as more performant computational procedures.

Only through these improvements it was possible to reproduce the dynamics from the experiment and gain a deeper insight into the self-truncated ionization injection regime.

Moreover, this interplay also revealed the limits of current laboratory diagnostics. Synthetic in-situ radiation diagnostics in PIConGPU spurred the development of new diagnostic methods for experiments. For example, the shift in laser focus position due to self-focusing in the plasma can now be quantified by spectral radiation signatures. Applying these new methods will enable an even more accurate understanding of laser plasma dynamics in experiments in the near future.

Keywords: radiation; LWFA; particle-in-cell; PIConGPU; synthetic diagnostics

  • Poster
    Advanced Accelerator Concepts 2018 (AAC 2018), 12.-17.8.2018, Breckenridge, Colorado, United States

Permalink: https://www.hzdr.de/publications/Publ-28520
Publ.-Id: 28520


Transverse electron beam dynamics in the beam loaded regime

Koehler, A.; Pausch, R.; Couperus Cabadağ, J. P.; Zarini, O.; Krämer, J.; Kurz, T.; Debus, A.; Bussmann, M.; Schramm, U.; Irman, A.

GeV electrons show the extraordinary advances of laser-wakefield acceleration (LWFA). Optimized beam parameters will enable drivers for compact secondary radiation sources. One essential key is a high quality electron bunch with low energy spread, small divergence and spot size. In this paper, the impact of beam loading on the transverse electron dynamic is systematically studied by investigating betatron radiation and electron beam divergence. The deployed LWFA setup yields reproducibly injected charges up to 0.5 nC and small energy spreads. The recorded betatron radiation reveals that the beam amplitude at the accelerator exit stays around one micron.

Keywords: LWFA; laser-wakefield acceleration; betatron source; beam loading; electron beam dynamics; laser-plasma interactions; x-ray

  • Lecture (Conference)
    16th International Conference on X-Ray Lasers (ICXRL), 07.-12.10.2018, Prag, Tschechische Republik

Permalink: https://www.hzdr.de/publications/Publ-28519
Publ.-Id: 28519


Compact X-ray sources by Traveling-Wave Thomson scattering and All-Optical FELs

Debus, A.; Steiniger, K.; Pausch, R.; Huebl, A.; Widera, R.; Siebold, M.; Loeser, M.; Albach, D.; Roeser, F.; Cowan, T.; Schramm, U.; Bussmann, M.

Compact synchrotron and SASE-FEL sources in the hard X-ray range require both compact electron accelerators and undulators. Traveling-Wave Thomson-Scattering (TWTS) provides an all-optical undulator with hundreds to thousands of undulator periods from high-power, pulse-front tilted lasers pulses. These allow to realize optical free-electron lasers (OFELs) with state-of-the-art technology in electron accelerators and laser systems.

We provide an overview on the applications that become possible with TWTS -- bright Thomson sources with high photon-yields, all-optical FELs and a novel class of laser-plasma accelerators not limited by dephasing and pump depletion. We outline both experimental and computational challenges and present recent results.

Keywords: Laser-produced plasmas; Plasma-based accelerators; Laser-wakefield acceleration; Traveling-wave electron acceleration; TWEAC

  • Lecture (Conference)
    16th International Conference on X-Ray Lasers (ICXRL), 07.-12.10.2018, Prag, Tschechische Republik

Permalink: https://www.hzdr.de/publications/Publ-28518
Publ.-Id: 28518


Off-harmonic optical probing of high intensity laser-matter interaction with a stand-alone probe laser system

Bernert, C.; Kraft, S.; Loeser, M.; Metzkes-Ng, J.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Siebold, M.; Zeil, K.; Ziegler, T.; Schramm, U.

The development of high-intensity short-pulse lasers in the petawatt regime offers the possibility to design new compact accelerator schemes by utilizing high-density targets to generate proton beams with multiple 10 MeV energy per nucleon. The optimization of the acceleration process calls for a comprehensive exploration of the plasma dynamics involved, for example via spatially and temporally resolved optical probing. Experimental results can then be compared to numerical particle-in-cell simulations, which is particularly well suited in the case of cryogenic hydrogen jet targets [1]. However, strong plasma self-emission and conversion of the plasma’s drive laser wavelength into its harmonics often masks the interaction region and interferes with the data analysis. Recently, the development of a stand-alone and synchronizable probe laser system for off-harmonic probing at the DRACO laser at the Helmholtz-Zentrum Dresden – Rossendorf showed promising performance [2]. Here, we present an updated stand-alone probe laser system applying a compact CPA system based on a synchronized fs mode-locked oscillator (Light Conversion) operating at 1030 nm, far off the plasma’s drive laser wavelength of 800 nm. A chirped volume Bragg grating (Optigrate Corp) is used as a hybrid stretcher and compressor unit. The subsequent diode pumped regenerative Yb:CaF2 laser amplifier includes a spectral shaping element and chirped mirrors for GDD compensation. The system delivers 160 fs pulses with a maximum energy of 0.9 mJ and thus extends the recent developments [3] into the sub 200 fs region. Additionally, we present recent experimental results deploying the upgraded probe laser system and its harmonics in an experiment dedicated to laser-proton acceleration from a renewable cryogenic hydrogen jet at the DRACO laser.

  • Lecture (Conference)
    ICUIL 2018, 09.-14.09.2018, Lindau, Deutschand

Permalink: https://www.hzdr.de/publications/Publ-28517
Publ.-Id: 28517


Probing of laser-plasma experiments at DRACO with a stand-alone probe laser system

Bernert, C.; Brack, F.-E.; Kraft, S.; Kroll, F.; Löser, M.; Metzkes-Ng, J.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Siebold, M.; Zeil, K.; Ziegler, T.; Schramm, U.

In the last decade the investigation of laser-driven plasmas has gained great importance for the development of compact ion accelerator schemes with the efficient generation of multiple 10 MeV proton beams from TNSA experiments with PW laser systems like the Dresden laser acceleration source (DRACO) at the Helmholtz-Zentrum Dresden - Rossendorf. The exploration of the plasma dynamics and its microscopic parameters is crucial for the optimization of the acceleration process. Optical probing is one technique to investigate the temporal plasma evolution and complements numerical particle-in-cell simulations of the underlying physics. However, strong plasma self-emission at the driver lasers wavelength and its harmonics often masks the laser plasma interaction region and thus complicates the data analysis.
Here, we present the implementation of a stand-alone probe laser system, which is temporally synchronized to the DRACO laser. The probe laser system consisting of a seed laser and one regenerative amplifier is based on Yb:YAG and thus provides a fundamental wavelength of 1030 nm, which is different from the wavelength of the DRACO driver laser (800 nm) and its harmonics. We present the advantages of this probing approach, which was tested during an experimental campaign with wire targets of different materials and diameters in the µm range, and give an inside on the current challenges and developments of the probing system.

  • Lecture (Conference)
    DPG Frühjahrstagung Würzburg, 19.-23.03.2018, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28516
Publ.-Id: 28516


Froth properties and ist effect on lab-scale flotation of carbonaceous sedimentary apatite ore

Hoang, D. H.; Kupka, N.; Peuker, U. A.; Rudolph, M.

The froth ability, froth stability and the froth structure are strong influences in flotation process i.e. on
water recovery, bubble size, entrainment of gangue particle, flotation rate constants, grade and recovery. The labscale
flotation of rich apatite ore with a high mass pull leads to significant changes in pulp and froth properties over
time. The froth stability decreases with increasing the flotation time. These changes can be related to different solid contents, reagent concentration, froth heights and bubble size distributions. This study presents the results from froth studies and discussions on the particle size of fully liberated silicates and degree of entrainment based on automated mineralogy size-by-size analysis. The change of entrainment in a rich apatite ore batch flotation with time will describe more precisely by measuring froth properties using a Dynamic Foam Analyzer. It is concluded that the degree of entrainment is not only dependent on particle size but also the pulp density due to its effect on particle settling and also froth properties in varying resistance to particle drainage. Furthermore, entrainment models are applied to predict the effect of size, flotation time on entrainment.

Keywords: Froth properties; apatite flotation; Entrainment; automated mineralogy

  • Contribution to proceedings
    29th International Mineral Processing Congress, IMPC 2018, 17.-21.09.2018, Moscow, Russia
    Conference Proceeding: Canadian Institute of Mining, Metallurgy and Petro, 978-703022711-9, 1748-1757

Permalink: https://www.hzdr.de/publications/Publ-28515
Publ.-Id: 28515


Froth properties and entrainment in lab-scale flotation: A case of carbonaceous sedimentary phosphate ore

Hoang, D. H.; Heitkam, S.; Kupka, N.; Hassanzadeh, A.; Peuker, U. A.; Rudolph, M.

In flotation, the froth characteristics strongly influence the separation process as they are linked to water recovery, bubble size, entrainment of gangue particles, flotation rate constants and finally grade and recovery. In the case of a high-grade apatite ore with a high mass pull in lab-scale flotation, significant changes in pulp and froth properties occur, such that the froth stability decreases with increasing flotation time. These changes can be related to different particle and reagent concentrations. We describe the change of entrainment in a rich apatite ore batch flotation with time more precisely by measuring froth properties using a Dynamic Froth Analyzer (DFA). It is concluded that the degree of entrainment is not only dependent on particle size but also the pulp density due to its effect on particle settling and also froth properties in varying resistance to drainage. Through a combination of time-resolved dynamic froth analysis and automated mineralogy, we identify the dynamic effects governing in the froth and compare the entrainment results with existing models. Furthermore, our analyses offer novel support for the extension of the common understanding of the entrainment phenomena.

Keywords: Froth flotation; froth stability; apatite; entrainment; automated mineralogy; dynamic froth analysis (DFA)

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-28514
Publ.-Id: 28514


Importance of understanding structure-property relationships in Feldspar for Radiofluorescence dating

Sharma, S. K.; Fuchs, M.; Heitmann, J.; Gloaguen, R.

Feldspar is a common mineral that has been used efficiently for the past few decades for luminescence dating. The process of separation of Feldspar from rock mineral is a time consuming process, and requires an expertise with different chemical processes. The luminescence properties in Feldspar are controlled by the presence/absence of defect in the host lattice. In the present talk, i will discuss about the different defects, luminescence properties, and their dependence on the crystal structure of Feldspar. The work is carried out on three different samples, currently being used for radio-fluorescence dating.

Keywords: Feldspar; optical properties; luminescence dating; ESR

  • Invited lecture (Conferences)
    3rd IR-RF Workshop 2018, 26.-28.02.2018, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-28513
Publ.-Id: 28513


Gewinnung und Anreicherung von Molybdän aus niedrig konzentrierten sulfatischen Lösungen mittels Solventextraktion

Helbig, T.; Scharf, C.

Der sogenannte Theisenschlamm, ein Haldenmaterial der einstigen Kupferschieferverhüttung in der Region Mansfeld, besitzt neben den Hauptkomponenten Zink und Blei, auch geringe Konzentrationen von z.B. Molybdän, Rhenium und Germanium. Im r⁴-Projekt „Theisenschlamm“ erfolgt im ersten Schritt die Laugung dieses Materials, wobei Lösungen mit ca. 20 mg/L Molybdän erhalten werden. Zur anschließenden elementselektiven Weiterverarbeitung der Laugungslösung wird u.a. die Solventextraktion untersucht. Für die selektive Gewinnung von Molybdän wurden Organophosphorsäure- sowie Oximverbindungen verglichen und Cyanex 272 als vielversprechendstes Extraktionsmittel ausgewählt. Weiterführende Untersuchungen werden in einer kontinuierlichen Mixer-Settler-Anlage (MEAB MSU-0,5) durchgeführt. Die Einflüsse verschiedener Parameter, wie z.B. die Rückführung der Organik und die Volumenströme der beiden Phasen, auf die selektive Molybdän-Extraktion und Anreicherung sowie die Möglichkeit des Scrubbings und Strippens der organischen Phase werden vorgestellt.

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Extraktion & Rohstoffe, 12.-13.03.2018, Frankfurt am Main, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28512
Publ.-Id: 28512


Laser-driven radiobiology experiments at Draco Petawatt

Brack, F.-E.; Kroll, F.; Metzkes, J.; Obst, L.; Kraft, S.; Schlenvoigt, H.-P.; Gaus, L.; Beyreuther, E.; Karsch, L.; Pawelke, J.; Zeil, K.; Schramm, U.

Summary of the current status and carried out experiments of Laser-driven radiobiology experiments at Draco Petawatt

  • Lecture (Conference)
    LIGHT Meeting, 19.-20.04.2018, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28511
Publ.-Id: 28511


Laser-Based Particle Accelerators at HZDR - Ions

Brack, F.-E.; Kroll, F.; Metzkes, J.; Obst, L.; Kraft, S.; Schlenvoigt, H.-P.; Gaus, L.; Ziegler, T.; Rehwald, M.; Zeil, K.; Schramm, U.

Summary of the current status and carried out experiments of Laser-driven ion experiments at Draco

  • Lecture (Conference)
    Matter and Technology Student Retreat, 11.06.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28510
Publ.-Id: 28510


Medical Applications of Laser-driven Particle Sources - An Overview of Activities in Dresden

Kroll, F.; Zeil, K.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Brack, F.; Metzkes-Ng, J.; Bernert, C.; Gaus, L.; Ziegler, T.; Kluge, T.; Garten, M.; Hübl, A.; Kraft, S.; Schramm, U.; Beyreuther, E.; Karsch, L.; Pawelke, J.; Kunz-Schughart, L.

The talk summarizes activities of HZDR on the topic of laser-driven particle sources for medical applications. The focus lies on a the development and characterization of a pulsed high-field beamline that allows to transport and spacially as well as spectrally shape a laser-driven ion beam and thereby prepare it for irradiation studies, e.g. on radiobiological studies.

  • Lecture (Conference)
    WHELMI Meeting 2018, 28.08.2018, Rehovot, Israel

Permalink: https://www.hzdr.de/publications/Publ-28509
Publ.-Id: 28509


Pulsed High-Field Magnets for a laser-driven Ion Beam shaping and Laboratory Astrophysics

Brack, F.-E.; Kroll, F.; Metzkes-Ng, J.; Gaus, L.; Kraft, S.; Schlenvoigt, H.-P.; Karsch, L.; Pawelke, J.; Zherlitsyn, S.; Herrmansdörfer, T.; Zeil, K.; Schramm, U.

Pulsed high-field magnets have become a common, versatile research tool. We present a pulsed magnet technology platform that opens up new areas of application in the field of laser-driven plasma physics. Compact high-field magnets, generating ms-long magnetic field pulses with amplitudes ranging as high as 20 T, have been developed for operation under high vacuum and in close vicinity to the harsh laser-plasma environment. The combination of the presented magnet technology and portable pulsed power systems paves the way for novel experiments in laboratory astrophysics and enables unique studies on beam optics for laser-driven ion sources.
We implemented a tunable pulsed beamline at the Dresden laser acceleration source (Draco) for radiobiological irradiation studies. It consists of two pulsed solenoids for shaping laser-accelerated ion beams spatially and spectrally for application. We performed experiments with the PW beam of Draco to investigate the feasibility of worldwide first controlled volumetric in vivo tumour irradiations in a dedicated mouse model with laser-accelerated protons. The study shows the reliable generation of homogeneous dose distributions laterally and in depth. Practical issues, like magnet repetition rate and stability, mean dose rate and future radiobiological challenges will be discussed and an outlook on the already performed volumetric tumour irradiation experiments will be given.
Furthermore, a split-pair coil was developed that can be used for the investigation of magnetized plasma in the frame laboratory astrophysical phenomena. The magnet provides optical access to the magnetized laser-driven plasma via two bores perpendicular to the coil axis. These openings enable optical and X-ray probing as well as insertion of obstacles and/or laser targets from solids to gas jets.

  • Lecture (Conference)
    ECLIM 2018, 22.-26.10.2018, Kreta, Griechenland
  • Poster
    Matter & Technology Meeting, 12.-14.06.2018, Berlin, Deutschland
  • Poster
    45th Conference on Plasma Physics EPS, 02.-06.07.2018, Prag, Tschechische Republik

Permalink: https://www.hzdr.de/publications/Publ-28508
Publ.-Id: 28508


Theisenschlamm – Waste of the past, resource of the future: a hydrometallurgical approach

Helbig, T.

A summary of the hydrometallurgical processing approach for "Theisenschlamm" was presented. The proposed approach was developed together with partners of the "Theisenschlamm" project. Limits and Challenges for the recovery of very low concentrated target elements were highlighted with examples of the solvent extraction processes.

  • Lecture (Conference)
    69. Berg- und Hüttenmännischer Tag – Freiberger Universitätsforum 2018, 06.-08.06.2018, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28507
Publ.-Id: 28507


Hydrometallurgical recovery of high-tech metals from a complex sulfidic flue dust with focus on the separation of rhenium and molybdenum by solvent extraction

Helbig, T.; Haseneder, R.; Werner, A.; Kelly, N.; Scharf, C.

“Theisenschlamm”, a flue dust of the former copper shale processing in Germany, comprises high amounts of zinc and lead as well as a variety of low concentrated high-tech metals, such as rhenium, molybdenum, cobalt and germanium. A hydrometallurgical process route was investigated to recover the valuable metals with focus on rhenium and molybdenum. However, very low concentrations of some target elements (1 – 15 mg/L) had to be considered. The process includes an innovative combination of membrane filtration and solvent extraction. With the first processing step 95% molybdenum were extracted from the pregnant leach solution in a continuous mixer settler set-up with the extractant Cyanex 272. High selectivity over rhenium was obtained, with a coextraction of only 0.3%. Continuous membrane nanofiltration technology achieved a selective separation and enrichment of 97.3% zinc, 98.5% iron(III), 97.0% copper, 98.3% aluminium and 99.1% cobalt over rhenium (7.2%) and germanium (7.7%). From the permeate solution 98.4% germanium were separated from rhenium (0.1%) by a continuous reverse osmosis membrane process. Extraction of 99.9% rhenium was obtained by continuous solvent extraction with Alamine 336. Considerations for the selective enrichment of very low concentrated target elements by solvent extraction are discussed in detail. Moreover, potential solvent extraction processes are suggested for further processing of the cobalt, germanium, zinc and copper containing membrane process streams.

  • Contribution to proceedings
    Hi-Tech Metals '18, 22.-23.11.2018, Cape Town, South Africa
  • Lecture (Conference)
    Hi-Tech Metals '18, 22.-23.11.2018, Cape Town, South Africa

Permalink: https://www.hzdr.de/publications/Publ-28506
Publ.-Id: 28506


Exploration of Rare Earth Elements and Absorption-Emission Features in Rare Earth (La-Lu) Orthophosphates

Sharma, S. K.; Koehler, T.; Fuchs, M.; Beyer, J.; Seidel, P.; Lorenz, S.; Meyer, D. C.; Gloaguen, R.; Heitmann, J.

Mining of rare earth elements (REEs) followed by application of mined REEs to wide range of application, has been of immense interest for both, geologists and phosphor engineers. In the present contribution, we will focus on a) exploring laser-induced fluorescence (LIF) for REE exploration in our project “inSPECtor”; and b) combining absorption-emission characteristics to understand f-f and f-d transitions in rare earth orthophosphates (La-Lu)PO4. Orthophosphate deposits in nature are important for technological and environmental challenges faced by high-tech industry. It has been shown recently that the phosphorites can be considered as the primary source of REEs to solve the global rare earth supply shortage [1]. The existing technologies in rare earth exploration are based on diffuse-reflectance measurements (for example, Hyperspectral Imaging). However, the spectral features of REEs are due to sharp 4f-4f intraconfigurational transitions, which are sufficiently distinct to enable spectral classification. LIF is an important technique which records REE features in spectral as well as the time domain. Recently, we started a project “inSPECtor” to develop a single sensor system, which combines hyperspectral imaging (or diffuse reflectance spectra) with laser induced fluorescence (for spectral and time resolution from ns to ms). From an application point of view, the Rare earth orthophosphates (REPO4) are important compounds for application in light emitting diodes (LEDs), plasma display panels (PDPs) and fluorescent lamps [2]. The lower atomic number lanthanides (La-Gd) based orthophosphates crystallise with monoclinic structure (P21/n space group) at moderately high temperatures; while the higher atomic number lanthanides based orthophosphates possess tetragonal xenotime-type structure (I41/amd space group). The luminescence properties in a lattice of orthophosphates are expected to be controlled by the type of REEs and their coordination around PO43- tetrahedra. However, PO43- (which forms host valence and conduction band), is transparent itself in visible-UV region and does not absorb, up to approximately 175 nm [3]. Hence, the type of rare earth ion, which increases in ionic radii by approximately 22% from La-Lu, control the electronic structure and optical properties therein. Some of the REPO4, for example-LaPO4, GdPO4, YPO4 and LuPO4; have been explored recently for their charge carrier trapping and relevant applications in storage devices [4]. However, information for other REPO4 is limited and no clear information, relevant to their absorption-emission features, charge storage/release could be found. We present results on our extensive investigation in both these directions; the new sensor and fundamental properties.

References:
[1] P. Emsbo, P.I.McLaughlin, G.N.Breit, E.A.du Bray, A.E.Koenig, Gondwana Res., 27 (2015) 776-785.
[2] J. George, C.Ryan, R.K.Brow, J. Am. Ceram. Soc. 97 (2014) 2249-2255.
[3] P.Melnikov, A.M.Massabni, O.Malta, Phosphorus, Sulfur and Silicon and Related Elements, 1996, pp. 1-1.
[4] T.Lyu, P.Dorenbos, J.Mater.Chem. C, 6 (2018) 369-379.

Keywords: Rare earth orthophosphates; laser induced fluorescence; exploration; diffuse reflectance

  • Lecture (Conference)
    The 5th International Conference on the Physics of Optical Materials and Devices (ICOM-2018), 27.-31.08.2018, Igalo, Montenegro, Montenegro

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-28505
Publ.-Id: 28505


Modeling Hybrid Wakefield Accelerators with PIConGPU

Debus, A.; Pausch, R.; Huebl, A.; Bastrakov, S.; Widera, R.; Martinez De La Ossa, A.; Irman, A.; Couperus, J.; Schramm, U.; Bussmann, M.

Hybrid LWFA-PWFA obtain high-charge beams of several 100pC with comparably large energy spread and divergence from a first LWFA stage. These beams are then used as a driver in a subsequent PWFA stage, where electron beams with less charge, but higher beam brightness are accelerated. Recent experiments at the HZDR, based on a LWFA-PWFA setup that includes an additional metal foil in between the gas jets, have provided promising results. The presence of very different regimes in hybrid LWFA-PWFAs ranging from underdense plasma to overdense plasma of the foil, interspersed with extended vacuum propagation distances is challenging for 3D-PIC simulations with regard to HPC resources, performance, numerical stability and the ability to iteratively compare with experimental results. The poster presents current simulation efforts at HZDR together with DESY collaborators in modeling experimental results using the open-source, 3D-PIC code PIConGPU. This includes simulation results from parameter scans, as well as the numerical techniques used.

Keywords: Laser-wakefield acceleration; Plasma-wakefield acceleration; PIC; PIConGPU; hybrid LPWFA; hybrid LWFA-PWFA; HPC; LWFA. PWFA

  • Poster
    Directions in particle beam-driven plasma wakefield acceleration, 04.-5.6.2018, Chicheley Hall, Großbrittannien

Permalink: https://www.hzdr.de/publications/Publ-28504
Publ.-Id: 28504


Traveling-Wave Electron Acceleration, Optical FELs and Thomson Scattering -- Designing laser pulses with a (pulse-front) tilt

Debus, A.; Steiniger, K.; Siebold, S.; Bussmann, M.; Pausch, R.; Albach, D.; Loeser, M.; Roeser, F.; Huebl, A.; Widera, R.; Cowan, T.; Schramm, U.

Generating and controlling ultrashort, pulse-front tilted laser pulses is essential for Traveling-Wave Electron Acceleration (TWEAC), Traveling-Wave Thomson Scattering (TWTS) and Traveling-Wave Optical FELs (TWTS-OFELs). All these applications require controlling angular and group-delay dispersion, while keeping experimental setups as compact as possible. However, the varying requirements with respect to laser power, extent of focal region, incident angles and laser mode quality lead to differing strategies in designing experimental setups.

In this overview poster we provide answers to the question: What experimental efforts in terms of laser system and optics are necessary in current labs for first proof-of-principle realizations of the different applications of "Traveling-Wave" laser pulses -- ranging from low-bandwidth and yield-enhanced Thomson sources (TWTS), laser-based electron accelerators beyond the LWFA depletion and dephasing limits (TWEAC) and ultimately an optical free-electron laser (TWTS-OFEL)?

Keywords: Laser-produced plasmas; Plasma-based accelerators; Laser-wakefield acceleration; Traveling-wave electron acceleration; TWEAC; optical FEL; traveling-wave; Thomson scattering; pulse-front tilt; out-of-focus interaction

  • Poster
    4. Annual MT Meeting, 12.-14.6.2018, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28503
Publ.-Id: 28503


Separation of rare earth elements from contaminants and valuable components by in situ precipitation during hydrometallurgical processing of eudialyte concentrate

Balinski, A.; Wiche, O.; Kelly, N.; Reuter, M. A.; Scharf, C.

Eudialyte - a sodium rich zirconosilicate - is often enriched in relevant amounts of Zr(Hf) as well as other valuable metals such as REE, Mn and Nb. Due to its ready solubility in mineral acids valuable components can be leached in high yields under mild conditions. The separation of individual elements from the resulting highly complex solutions can be very challenging, especially due to the release of silica. This study deals with REE separation by in situ precipitation during leaching of the thermal pre-treated H2SO4/eudialyte concentrate mixture. Contarary to the common procedure the precipitation was done before solid/liquid separation. Moreover, it was shown, that H2SO4 strongly affects the REE solubility and should be considered as a precipitating agent. The best REE precipitation yield of 90% was achieved by the following parameter combination: TP=95 °C, tP=120 min, ϱPD,P=150 kg/m3, βNa2SO4,0=116.4 g/L and βH2SO4,0=463.6 g/L. Not only LREE but also HREE+Y group could be removed from the liquid phase in high yields and separated from Zr(Hf), Mn, Nb, Fe and Al. After the precipitation step REE were transferred into the liquid phase by two different methods. Direct water treatment leads to decrease of the separation factors βSREE/(Zr,Hf,Mn,Nb) and βSREE/(Al,Fe,Th,Ca) with growing solid/liquid ratio due to remaining filtrate in the precipitate enriched in REE, and co-precipitation of Ca and Th. Conversion of precipitated REE into sparingly soluble hydroxides and subsequent HCl treatment improves the purity of the REE solution significantly. At a solid content of 200 kg/m3 the separation factors could be increased from 2.7 and 0.48 to 38.7 and 1.50, respectively. The great advantage of this method is the effective REE separation during leaching process by the use of basics chemicals only, and it is a good alternative for other separation methods such as solvent extraction.

Keywords: Eudialyte concentrate; sulfuric acid leaching; separation of rare earth elements; precipitation; double sulfates

Permalink: https://www.hzdr.de/publications/Publ-28502
Publ.-Id: 28502


Breaking the dephasing and depletion limits of laser-wakefield acceleration with Traveling-Wave Electron Acceleration

Debus, A.; Pausch, R.; Hübl, A.; Steiniger, K.; Widera, R.; Cowan, T.; Schramm, U.; Bussmann, M.

We show how to simultaneously solve several long standing limitations of laser-wakefield acceleration that have thus far prevented laser-plasma electron accelerators (LWFA) to extend into the energy realm beyond 10 GeV. Most prominently, our novel Traveling-Wave Electron Acceleration (TWEAC) approach eliminates both the dephasing and depletion constraints. The wakefield driver is a region of overlap of two obliquely incident, ultrashort laser pulses with tilted pulse-fronts in the line foci of two cylindrical mirrors, aligned to coincide with the trajectory of subsequently accelerated electrons. TWEAC leads to quasistatic acceleration conditions, which do not suffer from laser self-phase modulation, parasitic self-injection or other plasma instabilities. Particularly, and in contrast to LWFA and PWFA, a single TWEAC-stage can arbitrarily be extended in length to higher electron energies without changing the underlying acceleration mechanism. We introduce the new acceleration scheme, show results from 3D particle-in-cell simulations using PIConGPU, discuss energy scalability for both laser and electrons and elaborate on experimental realization requirements.

Keywords: Laser-produced plasmas; Plasma-based accelerators; Laser-wakefield acceleration; Traveling-wave electron acceleration; TWEAC

  • Lecture (Conference)
    DPG-Frühjahrstagung 2018, 19.-23.3.2018, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28501
Publ.-Id: 28501


Predictive geometallurgy: An interdisciplinary key challenge for mathematical geosciences

van den Boogaart, K. G.; Tolosana-Delgado, R.

Predictive geometallurgy tries to optimize the mineral value chain based on a precise and quantitative understanding of: the geology and mineralogy of the ores, the minerals processing, and the economics of mineral commodities. This chapter describes the state of the art and the mathematical building blocks of a possible solution to this problem. This solution heavily relies on all classical fields of mathematical geosciences and geoinformatics, but requires new mathematical and computational developments. Geometallurgy can thus become a new defining challenge for mathematical geosciences, in the same fashion as geostatistics has been in the first 50 years of the IAMG.

Keywords: Geostatistics; Statistical scales; Microstructure; Computational geometry; Processing optimisation; Value of information; Mineral liberation analyser; QUEMSCAN

  • Open Access Logo Book chapter
    Daya Sagar, B.S.; Cheng, Qiuming; Agterberg, Frits: Handbook of Mathematical Geosciences: Fifty Years of IAMG, Cham: Springer, 2018, 978-3-319-78998-9, 673-686
    DOI: 10.1007/978-3-319-78999-6_33

Permalink: https://www.hzdr.de/publications/Publ-28500
Publ.-Id: 28500


Control concepts for image-based structure tracking with ultrafast electron beam X-ray tomography

Windisch, D.; Bieberle, M.; Bieberle, A.; Hampel, U.

In this paper, a novel approach for tracking moving structures in multiphase flows over larger axial ranges is presented, which at the same time allows imaging the tracked structures and their environment. For this purpose, ultrafast electron beam X-ray computed tomography (UFXCT) is being extended by an image-based position control. Application is scanning and tracking of e.g. bubbles, particles, waves and other features of multiphase flows within vessels and pipes. Therefore, the scanner has to be automatically traversed with the moving structure basing on real-time scanning, image reconstruction and image data processing. In this paper we discuss requirements and different strategies for reliable object tracking. Promising tracking strategies have been numerically implemented and evaluated.

Keywords: Ultrafast X-ray computed tomography; structure tracking; multiphase flow; model predictive control

Permalink: https://www.hzdr.de/publications/Publ-28499
Publ.-Id: 28499


New Frontiers in Spectral-Spatial Hyperspectral Image Classification: The Latest Advances Based on Mathematical Morphology, Markov Random Fields, Segmentation, Sparse Representation, and Deep Learning

Ghamisi, P.; Maggiori, E.; Li, S.; Souza, R.; Tarabalka, Y.; Moser, G.; de Giorgi, A.; Fang, L.; Chen, Y.; Chi, M.; Serpico, S. B.; Benediktsson, J. A.

Airborne and spaceborne hyperspectral imaging systems have advanced in recent years in terms of spectral and spatial resolution, which makes data sets produced by them a valuable source for land-cover classification. The availability of hyperspectral data with fine spatial resolution has revolutionized hyperspectral image classification techniques by taking advantage of both spectral and spatial information in a single classification framework. The ECHO (Extraction and Classification of Homogeneous Objects) classifier, which was proposed in 1976, might be the first spectral-spatial classification approach of its kind in the remote sensing community. Since then and especially in the latest years, increasing attention has been dedicated to developing sophisticated spectral-spatial classification methods.
There is now a rich literature on this particular topic in the remote sensing community, composing of several fast-growing branches. In this paper, the latest advances in spectral-spatial classification of hyperspectral data are critically reviewed. More than 25 approaches based on mathematical morphology, Markov random fields, segmentation, sparse representation, and deep learning are addressed with an emphasis on discussing their methodological foundations. Examples of experimental results on three benchmark hyperspectral data sets, including both well-known long-used data and a recent data set resulting from an international contest, are also presented. Moreover, the utilized training and test sets for the aforementioned data sets as well as several codes and libraries are also shared online with the community.

Permalink: https://www.hzdr.de/publications/Publ-28498
Publ.-Id: 28498


Oscillating hydrogen bubbles at microelectrodes

Bashkatov, A.; Yang, X.; Hossain, S. S.; Mutschke, G.; Eckert, K.

Hydrogen produced via water electrolysis, which is powered by renewable energy, is an important energy carrier which may contribute to bridge the storage problem. However, the efficiency of alkaline water electrolyzers is not yet satisfying. Major reasons are the blockage of the active electrode area and the increase the ohmic resistance by the gas bubbles produced.
A deeper understanding of the mechanism of hydrogen bubble evolution therefore may provide additional opportunities to control and enhance the process. Microelectrodes which allow the inspection of single hydrogen bubble evolution are an interesting tool for that purpose [1].
Shadowgraphy and micro-PIV techniques, coupled to measurements of the electric current under potentiostatic mode at a 100 µm Pt electrode led to observation of a novel dynamic phenomenon. This consists in an oscillatory behavior of the hydrogen bubbles at the electrode, which depends on the applied potential and the concentration of the acidic electrolyte. With increasing potential a transition from periodic upward and downward movements of the bubble towards bubble shape oscillations is observed. This phenomenon is connected with the formation of a carpet of a small bubbles at the foot of the growing bubble and includes an oscillatory form of the Marangoni convection recently found on hydrogen bubbles [2]. Two possible candidates for the driving mechanism of the oscillations are discussed.
References:
[1] Yang, Xuegeng, et al. Dynamics of single hydrogen bubbles at a platinum microelectrode. Langmuir 31.29 (2015): 8184-8193.
[2] Yang, Xuegeng, et al. Marangoni convection at electrogenerated hydrogen bubbles. Physical Chemistry Chemical Physics 20.17 (2018): 11542-11548.

Keywords: electrolysis; hydrogen bubble; oscillations; electric force

  • Lecture (Conference)
    90th Annual Meeting of the International Association of Applied Mathematics and Mechanics. The International Association of Applied Mathematics and Mechanics (GAMM e.V.), 18.-22.02.2019, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-28496
Publ.-Id: 28496


Airlift Reactor – Experiment and CFD Simulation

Hessenkemper, H.; Ziegenhein, T.

Airlift reactors are modified bubble columns, where internal walls separate the up- and downward flow sections. Since appropriate experiments with locally resolved flow parameters are hardly available, a CFD-grade dataset has been created to validate the HZDR baseline closure model set for an internal airlift reactor. The measurements include many important gas-liquid flow characteristics like gas volume fraction, liquid velocity, turbulence parameters and bubble size distributions for both, the riser and the downcomer. CFD simulations of the test facility were conducted using the URANS concept and compared to the experiments to show strengths and drawbacks of the used closure models. The results reveal that the CFD simulations are capable to predict void fraction in the riser as well as the liquid velocity over the whole cross section quite well. However, the void fraction along the downcomer could not be reproduced in the simulations.

  • Poster
    16th Multiphase Flow Conference and Short Course, 13.-16.11.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28495
Publ.-Id: 28495


Feature Extraction and Selection of Sentinel-1 Dual-Pol Data for Global-Scale Local Climate Zone Classification

Hu, J.; Ghamisi, P.; Zhu, X. X.

The concept of the local climate zone (LCZ) has been recently proposed as a generic land-cover/land-use classification scheme. It divides urban regions into 17 categories based on compositions of man-made structures and natural landscapes. Although it was originally designed for temperature study, the morphological structure concealed in LCZs also reflects economic status and population distribution. To this end, global LCZ classification is of great value for worldwide studies on economy and population. Conventional classification approaches are usually successful for an individual city using optical remote sensing data. This paper, however, attempts for the first time to produce global LCZ classification maps using polarimetric synthetic aperture radar (PolSAR) data. Specifically, we first produce polarimetric features, local statistical features, texture features, and morphological features and compare them, with respect to their classification performance. Here, an ensemble classifier is investigated, which is trained and tested on already separated transcontinental cities. Considering the challenging global scope this work handles, we conclude the classification accuracy is not yet satisfactory. However, Sentinel-1 dual-Pol SAR data could contribute the classification for several LCZ classes. According to our feature studies, the combination of local statistical features and morphological features yields the best classification results with 61.8% overall accuracy (OA), which is 3% higher than the OA produced by the second best features combination. The 3% is considerably large for a global scale. Based on our feature importance analysis, features related to VH polarized data contributed the most to the eventual classification result.

Permalink: https://www.hzdr.de/publications/Publ-28494
Publ.-Id: 28494


Contamination effects on the lift force of ellipsoidal air bubbles rising in saline water solutions

Hessenkemper, H.; Ziegenhein, T.; Lucas, D.

The lift force is known to strongly influence the lateral bubble distribution in bubbly flows and is therefore an important force that has to be modeled in corresponding CFD simulations. For ellipsoidal bubbles, which are mostly present in industrial cases, the strength as well as the direction in which the lift force acts is determined by the bubble deformation. The bubble deformation however, can strongly be reduced when surface-active contaminations like salts are present in the liquid bulk, which implies a change of the lift force by contaminations too. In the present work, lift coefficients for single bubbles rising in aqueous NaCl solutions were determined to investigate the influence of such an inorganic surfactant on the lift force. For this purpose, a recently developed method by Ziegenhein et al. [Int. J. Multiphase Flow, Vol. 108, 11-24 (2018)] is used, which is capable to measure the lift force in low viscous liquids. Besides the lift force, the bubble shape and slip velocity were studied in detail to connect the results to known contamination effects, which showed different behavior in dependence on the salt concentration. The results reveal that the contamination level plays an important role on changes of the lift force in comparison to clean bubbles. Up to a concentration of 1.0 mol/l the salt has only a weak effect on the lift force of larger bubbles. The lift coefficients of smaller bubbles however, clearly show significant changes, which were also reflected in a change of the bubble shape. However, some findings could only be connected to the slip velocity, which implies a connection of the lift force to more than just the shape.

Keywords: Lift coefficient; Bubbly flows; Contaminations; Bubble shape; Slip velocity; Sodium chloride

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Permalink: https://www.hzdr.de/publications/Publ-28493
Publ.-Id: 28493


Radiometric Normalization of Multitemporal and Multisensor Remote Sensing Images Based on a Gaussian Mixture Model and Error Ellipse

Ghanbari, H.; Homayouni, S.; Ghamisi, P.; Safari, A.

Relative radiometric normalization is often required in time series analysis of satellite Earth observations such as land cover change detection. Normalization process reduces the radiometric differences caused by changes in the environmental conditions during the acquisition of multitemporal satellite images. In this paper, we proposed an efficient and automatic method based on Gaussian mixture model (GMM) to find a set of subjectively chosen invariant pixels. A linear model, based on Error Ellipse, was then adjusted to normalize the subject image. The proposed method involves two main steps; in the first step, invariant pixels, which are known as most probable unchanged pixels, were obtained by analyzing image differences estimated by GMMs. Then, these pixels were used to model the relationship between two multitemporal images. To evaluate the proposed method in real analysis scenarios, three multitemporal datasets acquired by different satellite sensors such as Ikonos, Quickbird, SuperView-1, and Worldview-2 were analyzed. These images were collected before and after the 2011's Japan and the 2004's Indonesia Tsunamis, and the 2017's Iran–Iraq earthquake. Experimental results demonstrated that the proposed method can considerably improve the radiometric variations between temporal images for change detection applications.

  • IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 11(2018)11, 4526-4533
    DOI: 10.1109/JSTARS.2018.2871373

Permalink: https://www.hzdr.de/publications/Publ-28491
Publ.-Id: 28491


Feature importance analysis for Local Climate Zone classification using a residual convolutional neural network with multi-source datasets

Qiu, C.; Schmitt, M.; Mou, L.; Ghamisi, P.; Zhu, X. X.

Global Local Climate Zone (LCZ) maps, indicating urban structures and land use, are crucial for Urban Heat Island (UHI) studies and also as starting points to better understand the spatio-temporal dynamics of cities worldwide. However, reliable LCZ maps are not available on a global scale, hindering scientific progress across a range of disciplines that study the functionality of sustainable cities. As a first step towards large-scale LCZ mapping, this paper tries to provide guidance about data/feature choice. To this end, we evaluate the spectral reflectance and spectral indices of the globally available Sentinel-2 and Landsat-8 imagery, as well as the Global Urban Footprint (GUF) dataset, the OpenStreetMap layers buildings and land use and the Visible Infrared Imager Radiometer Suite (VIIRS)-based Nighttime Light (NTL) data, regarding their relevance for discriminating different Local Climate Zones (LCZs). Using a Residual convolutional neural Network (ResNet), a systematic analysis of feature importance is performed with a manually-labeled dataset containing nine cities located in Europe. Based on the investigation of the data and feature choice, we propose a framework to fully exploit the available datasets. The results show that GUF, OSM and NTL can contribute to the classification accuracy of some LCZs with relatively few samples, and it is suggested that Landsat-8 and Sentinel-2 spectral reflectances should be jointly used, for example in a majority voting manner, as proven by the improvement from the proposed framework, for large-scale LCZ mapping.

Permalink: https://www.hzdr.de/publications/Publ-28490
Publ.-Id: 28490


Nonlinear plasmonic response of doped nanowires observed by infrared nanospectroscopy

Lang, D.; Balaghi, L.; Winnerl, S.; Schneider, H.; Hübner, R.; Kehr, S. C.; Eng, L. M.; Helm, M.; Dimakis, E.; Pashkin, A.

We report a strong shift of the plasma resonance in highly doped GaAs/InGaAs core/shell nanowires for intense infrared excitation observed by scattering-type scanning near-field infrared microscopy. The studied nanowires show a sharp plasma resonance at a photon energy of about 125 meV in the case of continuous-wave excitation by a CO₂ laser. Probing the same nanowires with the pulsed free-electron laser with peak electric field strengths up to several 10 kV/cm reveals a power-dependent redshift to about 95 meV and broadening of the plasmonic resonance. We assign this effect to a substantial heating of the electrons in the conduction band and subsequent increase of the effective mass in the nonparabolic Γ-valley.

Keywords: nonlinear plasmonics; infrared nanospectroscopy; s-SNIM; free-electron laser; nanowires; InGaAs

Permalink: https://www.hzdr.de/publications/Publ-28489
Publ.-Id: 28489


Hyperspectral and LiDAR Fusion Using Deep Three-Stream Convolutional Neural Networks

Li, H.; Ghamisi, P.; Soergel, U.; Zhu, X. X.

Recently, convolutional neural networks (CNN) have been intensively investigated for the classification of remote sensing data by extracting invariant and abstract features suitable for classification. In this paper, a novel framework is proposed for the fusion of hyperspectral images and LiDAR-derived elevation data based on CNN and composite kernels. First, extinction profiles are applied to both data sources in order to extract spatial and elevation features from hyperspectral and LiDAR-derived data, respectively. Second, a three-stream CNN is designed to extract informative spectral, spatial, and elevation features individually from both available sources. The combination of extinction profiles and CNN features enables us to jointly benefit from low-level and high-level features to improve classification performance. To fuse the heterogeneous spectral, spatial, and elevation features extracted by CNN, instead of a simple stacking strategy, a multi-sensor composite kernels (MCK) scheme is designed. This scheme helps us to achieve higher spectral, spatial, and elevation separability of the extracted features and effectively perform multi-sensor data fusion in kernel space. In this context, a support vector machine and extreme learning machine with their composite kernels version are employed to produce the final classification result. The proposed framework is carried out on two widely used data sets with different characteristics: an urban data set captured over Houston, USA, and a rural data set captured over Trento, Italy. The proposed framework yields the highest OA of 92.57% and 97.91% for Houston and Trento data sets. Experimental results confirm that the proposed fusion framework can produce competitive results in both urban and rural areas in terms of classification accuracy, and significantly mitigate the salt and pepper noise in classification maps.

Permalink: https://www.hzdr.de/publications/Publ-28488
Publ.-Id: 28488


A Flow Pattern Adaptive Multi-field Two-fluid Concept for turbulent two-phase flows

Schlegel, F.; Meller, R.; Oertel, R.

Industrial applications feature a huge variety of different flow patterns, such as bubbly flow, slug flow or annular flow. Thereby the issue of a big range of different physical scales is involved. With the objective of reproduction of occurring phenomena with one single multifluid solver, we present an Euler-Euler-approach, which combines a number of different methods for treatment of the partial aspects. The implementation into OpenFOAM is always with focus on sustainable research, including a state-of-the-art IT concept. A segregated approach is used for treatment of the phase momentum equations, phase fraction equations and the pressure equation, featuring a consistent momentum interpolation scheme (Cubero et al., 2014). To fulfill the kinematic condition at resolved interfaces between different continuous phases, the latter may be coupled either by an isotropic (Strubelj and Tiselj, 2011) or by an anisotropic drag. In both cases, the immensely strong phase coupling requires an adapted numerical method. State and evolution of bubble size distribution in disperse phase context is solved with either class or moment methods. The overall objective is to take interactions between the all different aspects, such as disperse phases, resolved interfaces and turbulence with effects on momentum and mass transfer into account.

  • Poster
    16th Multiphase Flow Conference and Short Course, 13.-16.11.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28487
Publ.-Id: 28487


Magnetoacoustic Relaxation by Cr2-+ Jahn–Teller Centers Revealed from Elastic Moduli

Gudkov, V. V.; Bersuker, I. B.; Zhevstovskikh, I. V.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Korostelin, Y. V.

Magnetoacoustic investigations of the ZnSe:Cr2+ crystal with sphalerite structure, performed in Faraday geometry, show that there is a new channel of relaxation by the Cr2+ Jahn–Teller (JT) centers, induced by the magnetic field. A new method is worked out that allows to extract the relaxation time, either from the temperature changes of the elastic modulus in fixed magnetic field or from the magnetic field dependences at fixed temperatures. Application of both approaches to the imaginary part of the elastic modulus prove their efficiency and indicate that the magnetic field dependent relaxation rate reaches the magnitude of about 106s-1 at T = 1.3 K.

Permalink: https://www.hzdr.de/publications/Publ-28486
Publ.-Id: 28486


Technical note: Co-localized (colloidal probe) atomic force microscopy / Raman spectroscopy measurements for floatability characterization

Babel, B.; Rudolph, M.

Atomic force microscopy measurements are chemically blind towards the underlying sample surface. On chemically heterogeneous samples e.g. ores the identification of regions of interest relies on the optical microscopic image and previous sample characterizations e.g. by a SEM + EDX combination. In this paper, we demonstrate for the first time the application of co-localized colloidal probe atomic force microscopy / Raman (CP-AFM-Raman) measurements, combining the wettability information of a cassiterite in a quartz matrix with the identification of the mineral phases by their Raman spectra at a high spatial resolution of only 1 µm. Additional topography measurements are performed highlighting the selective adsorption of sulfosuccinamate molecules, resulting in a nano-structuring of the cassiterite surface by collector molecules.

Keywords: Atomic force microscopy; hydrophobic interactions; Raman spectroscopy; flotation research; adsorption; cassiterite

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-28485
Publ.-Id: 28485


Fast preparation and recycling method for colloidal probe cantilevers in hydrophobic mapping applications

Babel, B.; Rudolph, M.

Probe contamination of atomic force microscope (AFM) tips with colloidal probes is limiting the lifetime of the probe and the reproducibility in force interaction measurements, rendering cantilevers useless. Earlier proposed cleaning methods like mechanical scrubbing, UV, plasma and solvent cleaning procedures have limitations especially for inorganic particulate contaminations. In this paper we demonstrate a fast procedure to recycle contaminated colloidal probe cantilevers and reequip them with pristine colloids without affecting the mechanical and structural properties of the cantilever. The proposed procedure reduces the total time for probe preparation and allows extended experimental test work with singular cantilevers reducing the deviations by cantilever calibration.

Keywords: Atomic force microcopy; recyclable cantilevers; fast colloidal probe preparation; adhesion imaging; contaminations

Permalink: https://www.hzdr.de/publications/Publ-28484
Publ.-Id: 28484


Investigating reagent-mineral interactions by colloidal probe atomic force microscopy

Babel, B.; Rudolph, M.

The characterization of reagent-mineral interactions in flotation systems of finely intergrown ores holds difficult challenges for the applicability of standard techniques like Hallimond tube tests and contact angle experiments or renders them impossible due to a lack of sufficient samples in terms of quality and quantity. This disadvantage may not apply to more sophisticated techniques, but these often do not work in an aqueous environment.
We present the utilization of an atomic force microscope with a hydrophobic colloidal probe to characterize the wettabilities of individual mineral domains of an ore sample, while additional spectral information is gathered by Raman spectroscopy. The exemplary ore sample investigated is mainly containing cassiterite and quartz, therefore the reference measurements like Hallimond tube tests and contact angle experiments were carried out with this binary system as a comparison.
The focus of the study lies in the correlation of data gathered by the atomic force microscope and the Raman spectrometer with data from standard techniques. Finally the applicability of the colloidal probe atomic force microcopy technique for reagent-mineral investigations is critically evaluated.

Keywords: Atomic force microscope; colloidal probe; hydrophobic interactions; Raman spectroscopy; cassiterite

  • Contribution to proceedings
    International Mineral Processing Congress, 17.-21.09.2018, Moskau, Russland
    International Mineral Processing Congress (IMPC 2018)
  • Lecture (Conference)
    International Mineral Processing Congress 2018, 19.09.2018, Moskau, Russland

Permalink: https://www.hzdr.de/publications/Publ-28483
Publ.-Id: 28483


Physical model of the Czochralski crystal growth in a horizontal magnetic field

Pal, J.; Grants, I.; Eckert, S.; Gerbeth, G.

The horizontal magnetic field (HMF) may improve conditions in the melt during large silicon single crystal growth by the Czochralski technique. This observation is counter-intuitive as the HMF evidently breaks the rotational symmetry. A previous study has shown that the HMF is not able to
significantly delay the Rayleigh-Bénard instability in a rotating cylinder [1]. It has been observed [2] that an oscillating flow sets in soon after the linear onset. Can we expect a stabilizing effect of the HMF in the Czochralski growth? Why the symmetry breaking by the HMF is eventually not
so relevant? These are two central questions for our primarily experimental study using the room-temperature eutectic alloy GaInSn for dedicated model experiments, allowing an almost complete measurement of the velocity field inside the melt [3]. Besides, it is also meant as a benchmark for comparison with the numerical codes. To serve the latter purpose the boundary conditions should be preferably well defined. Having this in mind the temperature boundary conditions are defined as follows. An isothermal heating is applied at the bottom of a cylindrical cell filled with GaInSn
alloy. The side wall is thermally insulated. An optionally rotating isothermal cooler models the growing crystal. A water-cooled layer of an alkaline solution keeps the rest of the metal surface free from oxides and models the radiation heat loss. The maximum HMF strength is 0.3 T that
corresponds to a Hartmann number of about 1200. Velocity profiles are measured by ultrasound Doppler velocimetry. Temperatures are monitored in the vicinity of the triple point at the rim of the cooler, at the rim of the cell, inside of the cooler and of the heater. The Nusselt-Grashof number
dependency is obtained by controlling the total heat flux injected at the bottom and measuring the temperature difference between the bottom plate and the cooler. The critical cooler rotation rate is determined at which the rotation introduces a significant variation of the velocity field dominated by the HMF-aligned convection rolls.

Keywords: Czochralski; Physical model; horizontal magnetic field

  • Open Access Logo Contribution to proceedings
    International Workshop on Modeling in Crystal Growth, 21.-24.10.2018, Kailua-Kona, Hawaii, USA
    Program of the 9 th International Workshop on Modeling in Crystal Growth
  • Lecture (Conference)
    International Workshop on Modeling in Crystal Growth, 21.-24.10.2018, Kailua-Kona, Hawaii, USA

Permalink: https://www.hzdr.de/publications/Publ-28481
Publ.-Id: 28481


Electroforming-free resistive switching in polycrystalline YMnO3 thin films

Rayapati, V. R.; Du, N.; Bürger, D.; Patra, R.; Skorupa, I.; Matthes, P.; Stöcker, H.; Schulz, S. E.; Schmidt, H.

Polycrystalline YMnO3 thin films sandwiched between an un-patterned bottom electrode (Pt or Pt/Ti) and a circular top electrode (Au or Al) reveal an electroforming-free, unipolar resistive switching. We report YMnO3 resistive switching devices endurance depending on the bottom electrode and the top electrode. The number of loading cycles of the Al/YMnO3/Pt resistive switch is larger than 103. The resistance ratio between the high resistance (OFF) and the low resistance (ON) state is larger than 104, which can be further increased to 105 by decreasing the diameter of the Al top electrode.

Permalink: https://www.hzdr.de/publications/Publ-28480
Publ.-Id: 28480


Dissipation-Induced Instabilities in Magnetized Flows

Kirillov, O. N.

We study local instabilities of a differentially rotating viscous flow of electrically conducting incompressible fluid subject to an external azimuthal magnetic field. A hydrodynamically stable flow can be destabilized by the magnetic field both in an ideal and a viscous and resistive system giving rise to the azimuthal magnetorotational instability. A special solution to the equations of ideal magnetohydrodynamics characterized by the constant total pressure, the fluid velocity parallel to the direction of the magnetic field, and by the magnetic and kinetic energies that are finite and equal—the Chandrasekhar equipartition solution—is marginally stable in the absence of viscosity and resistivity. Performing a local stability analysis, we find the conditions under which the azimuthal magnetorotational instability can be interpreted as a dissipation-induced instability of the Chandrasekhar equipartition solution.

Permalink: https://www.hzdr.de/publications/Publ-28479
Publ.-Id: 28479


A Flow Pattern Adaptive Multi-Field Two-Fluid Concept for Turbulent Two-Phase Flows

Meller, R.; Schlegel, F.; Lucas, D.

Industrial applications feature a huge variety of different flow patterns, such as bubbly flow, slug flow or annular flow. Thereby the issue of a big range of different physical scales is involved. With the objective of reproduction of occurring phenomena with one single multifluid solver, we present an Euler-Euler-approach, which combines a number of different methods for treatment of the partial aspects. The implementation into OpenFOAM is always with focus on sustainable research. A segregated approach is used for treatment of the phase momentum equations, phase fraction equations and the pressure equation, featuring a consistent momentum interpolation scheme (Cubero et al., 2014). To fulfill the kinematic condition at resolved interfaces between different continuous phases, the latter may be coupled by an isotropic drag (Strubelj and Tiselj, 2011). In this case, the immensely strong phase coupling requires an adapted numerical method. The overall objective is to take interactions between the all different aspects, such as disperse phases, resolved interfaces and turbulence with effects on momentum and mass transfer into account.

Keywords: computational fluid dynamics; two-fluid model; multiphase; numerical method

  • Lecture (others)
    Seminar des Instituts für Mathematik und Rechneranwendungen der Universität der Bundeswehr München, 09.02.2018, München, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28478
Publ.-Id: 28478


On machine learning algorithms and compositional data

Tolosana-Delgado, R.; Talebi, H.; van den Boogaart, K. G.

Predictive methods such as Lasso regression, partition trees and random forests (RF), artificial neural networks (ANN) and deep learning, or support-vector machines (SVM) and other kernel methods have become in the last years increasingly popular, also in the compositional data community. However, most of the contributions using machine learning algorithms on compositional data just applied the relevant method to an additive, centered or isometric log-ratio (alr, clr, ilr) transformed version of the training data, without caring about the properties of the construct. In this contribution we briefly review the fundamental construction of these methods, and check in which way can they be tweaked or adapted to account for the compositional scale of the data.

As an example, a binary partition tree aims at constructing a hierarchy of classification, where each branch splits the data in two subgroups according to the one single covariable that provides highest purity of the two resulting subgroups; at the end of the hierarchy, all branches contain only data from one pure group. Random Forests (Breiman, 2001) were introduced to deal with the obvious over-fitting of partition trees, with a double randomisation strategy: first bootstrapping the number of observations, creating B different trees that form the forest; second, each branching of each tree is based not on the whole set of variables, but on a different random subset of them. The fact that at each branching only one variable is actively used makes the method non-invariant under the choice of possible log-ratio transformations. A way to allow for this one feature selection while keeping the relative nature of compositional information would be to build the trees on the set of pairwise log-ratios (pwlr). This applies to all kinds of tree-based methods with compositional covariables.

Keywords: affine equivariance; subcompositional coherence; variable selection

  • Open Access Logo Contribution to proceedings
    8th International Workshop on Compositional Data Analysis, 03.-08.06.2019, Terrassa, Spanien

Permalink: https://www.hzdr.de/publications/Publ-28476
Publ.-Id: 28476


In vivo confirmation of altered hepatic glucose metabolism in patients with liver fibrosis/cirrhosis by 18F-FDG PET/CT

Verloh, N.; Einspieler, I.; Utpatel, K.; Menhart, K.; Brunner, S.; Hofheinz, F.; van den Hoff, J.; Wiggermann, P.; Evert, M.; Stroszczynski, C.; Hellwig, D.; Grosse, J.

Objective: The aim of this study was to assess the value of 18F-FDG PET/CT for quantitative assessment of hepatic metabolism in patients with different stages of liver fibrosis/cirrhosis. Materials and methods: 18F-FDG PET/CT scans of 37 patients either with or without liver fibrosis/cirrhosis, classified according to the METAVIR score (F0-F4) obtained from histopathological analysis of liver specimen, were analyzed retrospectively and classified as follows: no liver fibrosis (F0, n = 6), mild liver fibrosis (F1, n = 11), advanced liver fibrosis (F2, n = 6), severe liver fibrosis (F3, n = 5), and liver cirrhosis (F4, n = 11). The liver-to-blood ratio (LBR, scan time corrected for a reference time of 75 min) was compared between patient groups. Results: Patients with liver fibrosis or cirrhosis (≥ F1; LBR 1.53 ± 0.35) showed a significant higher LBR than patients with normal liver parenchyma (F0, 1.08 ± 0.23; P = 0.004). In direct comparison, LBR increased up to the advanced stage of liver fibrosis (F2; 2.00 ± 0.40) and decreased until liver cirrhosis is reached (F4, 1.32 ± 0.14). Conclusion: Functional changes in liver parenchyma during liver fibrosis/cirrhosis affect hepatic glucose metabolism and significantly differ between stages of liver fibrosis/cirrhosis, classified according to the METAVIR scoring system, as demonstrated by LBR quantification by 18F-FDG PET/CT.

Keywords: 18F-FDG PET/CT; FDG kinetics; Hepatic metabolism; Liver cirrhosis; Liver fibrosis; METAVIR score

Permalink: https://www.hzdr.de/publications/Publ-28475
Publ.-Id: 28475


U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions – Spectroscopic investigations of retention mechanisms

Philipp, T.; Shams Aldin Azzam, S.; Rossberg, A.; Huittinen, N.; Schmeide, K.; Stumpf, T.

Environmental conditions in deep geological repositories for radioactive waste may involve high pH values due to the degradation of concrete. However, the U(VI) sorption at such (hyper)alkaline conditions is still poorly understood. In this study, batch sorption experiments with Ca-bentonite in the pH range 8–13 at different carbonate concentrations were combined with spectroscopic investigations in order to gain insight into the underlying retention mechanisms. It was found that U(VI) sorption strongly correlates with the aqueous U(VI) speciation determined by time-resolved laser-induced luminescence spectroscopy (TRLFS). Increasing retention with increasing pH was accompanied by a change in aqueous speciation from uranyl carbonates to uranyl hydroxides. The occurrence of luminescence line -narrowing and a decreased frequency of the symmetric stretch vibration, deduced from site-selective TRLFS, indicate the presence of adsorbed U(VI) surface complexes. X-ray absorption fine structure (EXAFS) spectroscopy confirms that surface precipitation does not contribute significantly to the removal of U(VI) from solution but that retention occurs through the formation of two non-equivalent U(VI)-complexes on the bentonite surface. The present study demonstrates that in alkaline environments, where often only precipitation processes are considered, adsorption can provide effective retention of U(VI), despite the anionic character of prevailing aqueous species.

Keywords: uranium; Ca-bentonite; sorption; (hyper)alkaline; site-selective TRLFS; EXAFS; speciation; surface complexation

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Permalink: https://www.hzdr.de/publications/Publ-28474
Publ.-Id: 28474


Eulerian multiphase flow modelling: bubbly flow with phase change

Liao, Y.; Krepper, E.; Ding, W.

Phase change phenomena such as evaporation and condensation are encountered frequently in daily life and technical applications. However, reliable numerical simulation of these processes is still challenging mainly due to insufficient knowledge on the mechanism of interfacial mass, momentum and energy exchanges. In the context of two-fluid model, developing and applying general closures for the representation of interfacial structures and exchanging processes is of great significance. In the presentation the HZDR baseline modelling approach for poly-dispersed bubbly flow with details on bubble size, interfacial area density, sub-cooled wall boiling as well as interphase heat transfer coefficient will be introduced. Application examples for condensing, flash evaporating and wall boiling flows will be presented.

  • Invited lecture (Conferences)
    Lectures on multiphase CFD at Central South University, 06.-08.06.2018, Changsha, China

Permalink: https://www.hzdr.de/publications/Publ-28473
Publ.-Id: 28473


Turbulence-Interface Interaction in Large-Eddy Simulations with a Two-Fluid Model

Meller, R.; Klein, M.; Lucas, D.; Schlegel, F.

With the aim of a generalized model framework for two-phase flows, cases with large scale interfaces are modeled by means of a two-fluid model in the manner of large-eddy simulations. In this context a number of unclosed terms due to the filtering operation arise. One of them is the classical convective sub-grid scale turbulence stress term. Different closure models for the convective sub-grid scale term are adapted to the presented model framework and a-posteriori investigations are carried out in order to compare the influence of the different modeling approaches.

Keywords: computational fluid dynamics; two-fluid model; large-eddy simulation; multiphase; rising bubble

  • Contribution to proceedings
    12th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements, 26.-28.09.2018, Montpellier, Frankreich
  • Lecture (Conference)
    12th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements, 26.-28.09.2018, Montpellier, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-28472
Publ.-Id: 28472


On numerical simulation of flashing flows

Liao, Y.; Lucas, D.

Flashing of water into steam due to decompression or pressure loss is a familiar scenario during the LOCA accident of Light Water Reactors. Because of its relevance to the safety analysis there have been many research activities since the mid of last century. Nevertheless, the understanding of nucleation characteristics, bubble dynamics, as well as interphase exchanges remains insufficient, which makes it quite difficult to define the problem precisely in numerical simulations. As a result, a broad consensus on numerical methods for flashing flows is not available, and various models have been used even for the same case. For example, the critical flashing flow in a converging-diverging nozzle has been studied either with cavitation models or thermal phase change models, and there is little discussion on the contribution of mechanical and thermal effects under given temperature and pressure conditions. A guideline for selecting an appropriate model is desirable, which is clearly not an easy task due to complex physics and missing insights. Under the guidance of a baseline model concept presented in our previous work the present work will focus on the evaluation of existing numerical methods for flashing flows, and aim to discover the underlying laws with help of computational fluid dynamics and experimental data. The temporal and spatial distribution of evaporated steam will be reproduced numerically, and the effect of closure models for interphase exchanging rates as well as bubble dynamics will be discussed.

Keywords: closure model; computational fluid dynamics; flashing flow; numerical methods; phase change

  • Contribution to proceedings
    The 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-22.08.2019, Portland, USA
  • Lecture (Conference)
    The 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-22.08.2019, Portland, USA

Permalink: https://www.hzdr.de/publications/Publ-28464
Publ.-Id: 28464


Euler-Euler Simulation of Fluid Dynamics and Mass Transfer in Bubbly Flows

Rzehak, R.; Kappelt, C.

CFD simulations of dispersed bubbly flow on the scale of technical equipment are feasible within the Eulerian two-fluid framework of interpenetrating continua. However, accurate numerical predictions rely on suitable closure models. To achieve predictive capability, all details of the closure models have to be fixed in advance without reference to any measured data.
Concerning the fluid dynamics of bubbly flows a baseline model has recently been proposed to this end and shown to work for a range of different applications in a unified manner1,2. This provides a reliable background which is well suited to add more complex physics. Concerning mass transfer in bubbly flows only few studies have been performed to date3. For the mass transfer coefficient, a variety of entirely different closures have been applied in rather similar situations. To facilitate predictive applications, a standard model which is validated for a broad range of conditions yet has to be developed.
The present contribution considers two test cases from the literature, where mass transfer takes place during the absorption of oxygen into water. The first case is a bubbly mixing layer4, the second is concerned with co-current bubble column flow5. The above mentioned baseline model is used for the fluid dynamical part of the simulation model. Two different correlations for the mass transfer coefficient are considered6, which had been used in previous work. Sources of uncertainty in both, models and data, are discussed. Taking into account possible measurement errors, reasonable agreement between simulations and measurements is found for the present situations. Needs for further experimental data to facilitate qualification of a generally applicable model are specified.

Keywords: Euler-Euler simulation; dispersed gas-liquid multiphase flow; mass-transfer

  • Lecture (Conference)
    12th European Fluid Mechanics Conference, 09.-13.09.2018, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-28463
Publ.-Id: 28463


Euler-Euler modelling of bubble dynamics in flashing flows

Liao, Y.; Lucas, D.

A poly-disperse multiple-size-group approach, which is a class method of population balance, is developed for two-fluid modelling of the evolution of gas-liquid mixture during flash evaporation. Special efforts are dedicated to the development and validation of sub models for describing bubble nucleation, coalescence and breakup as well as interfacial heat transfer rates. The baseline model with a fixed set of closures for interphase momentum transfer and bubble-induced turbulence, which was proposed in the previous work and validated for isothermal cases, is extended by a mechanistic model for the overall heat transfer coefficient from liquid to gas-liquid interface, and the model for bubble growth and shrinkage due to phase change. The poly-disperse approach is applied to simulate evaporating pipe flow under pressure release transients, which is controlled by the operation of a blow-off valve. CFD-grade experimental data including local bubble size and void fraction as well as velocity distributions are available for model validation. The comparison demonstrates that the model is effective in capturing the temporal course of vapour bubbles’ generation and growth as well as their spatial distribution. The agreement between measured and simulated cross-section averaged flow parameters such as void fraction, liquid temperature and bubble size distribution is satisfying.

  • Contribution to proceedings
    10th International Conference on Multiphase Flow, ICMF2019, 19.-24.05.2019, Rio de Janeiro, Brazil
  • Lecture (Conference)
    10th International Conference on Multiphase Flow, ICMF2019, 19.-24.05.2019, Rio de Janeiro, Brazil

Permalink: https://www.hzdr.de/publications/Publ-28462
Publ.-Id: 28462


Euler-Euler Closure for Bubbly Flows with Full Reynolds Stress Model and Anisotropic Bubble-induced Turbulence

Rzehak, R.; Parekh, J.

In the present work, Euler-Euler modeling of bubbly flows is combined with a full Reynolds stress model for the turbulence in the liquid carrier phase. Reynolds stress models have only rarely been explored in this context, although effects requiring this level of description are frequently encountered in industrial applications towards which the Euler-Euler approach is geared. In particular, source terms describing the additional bubble-induced contribution to the liquid phase turbulence with proper account for its anisotropy have not firmly been established yet. A formulation based on the direction of bubble motion relative to the liquid is given here. Two well-known variants of Reynolds stress models due to Launder, Reece and Rodi and Speziale, Sarkar and Gatski are compared. Closure relations for the bubble forces are applied that have been shown previously to work well over a range of conditions. The model is validated by comparison with a set of pipe flow data that contains variations of liquid and gas flow rates as well as different pipe diameters. An important criterion for the selection of the data was to provide measurements of individual components of the Reynolds stress tensor.

Keywords: Euler-Euler simulation; dispersed gas-liquid multiphase flow; turbulence modeling; Reynolds-strss model; bubble-induced turbulence

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe CFD, 06.-07.03.2018, Bremen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28461
Publ.-Id: 28461


The year-long development of microorganisms in uncompacted Bavarian bentonite slurries at 30 °C and 60 °C

Matschiavelli, N.; Kluge, S.; Podlech, C.; Standhaft, D.; Grathoff, G.; Ikeda-Ohno, A.; Warr, L.; Chukharkina, A.; Arnold, T.; Cherkouk, A.

In the multi-barrier concept for the deep geological disposal of high-level radioactive waste (HLW), bentonite is proposed as a potential barrier and buffer material for sealing the space between the steel-canister containing the HLW and the surrounding host rock. In order to broaden the spectra of appropriate bentonites, we investigated the metabolic activity and diversity of naturally occurring microorganisms as well as their time-dependent evolution within the industrial B25 Bavarian bentonite under repository-relevant conditions. We conducted anaerobic microcosm-experiments containing the B25 bentonite and a synthetic Opalinus Clay pore water solution, which were incubated for one year at 30 °C and 60 °C. Metabolic activity was only stimulated by the addition of lactate, acetate or H2. The majority of lactate- and H2-containing microcosms at 30 °C were dominated by strictly anaerobic, sulfate-reducing and spore-forming microorganisms. The subsequent generation of hydrogen sulfide led to the formation of iron-sulfur precipitations. Independent from the availability of substrates, thermophilic bacteria dominated microcosms that were incubated at 60 °C. However, in the respective microcosms, no significant metabolic activity occurred and there was no change in the analyzed bio-geochemical parameters.

Keywords: high-level radioactive waste repository; sulfate-reduction; spores; thermophiles

Permalink: https://www.hzdr.de/publications/Publ-28460
Publ.-Id: 28460


Bio-Angeln zum Recycling von Elektroschrott

Lederer, F.

Bio-Angeln zum Recycling von Elektroschrott

  • Lecture (others)
    Geissinger Technikerstammtisch am HZDR, 7.11.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28459
Publ.-Id: 28459


Effect of pH on the Formation of Gibbsite-Layer Films at the Muscovite (001)−Water Interface

Lee, S. S.; Schmidt, M.; Sturchio, N. C.; Nagy, K. L.; Fenter, P.

Aluminum (oxy)hydroxide films play an important role as sorbents of toxic elements in aqueous environments, where their heterogeneous nucleation and growth can be controlled by the speciation of dissolved Al species and the charge and structure of underlying mineral surfaces. The structure of gibbsite films nucleated at the interface between the muscovite (001) surface and 1 mM AlCl3 solutions was investigated as a function of pH using in situ X-ray reflectivity. Growth of well-ordered gibbsite films was observed at pH 3–4, even when the solutions were undersaturated with respect to gibbsite. The ordering of these gibbsite films likely resulted from the structural similarity (i.e., epitaxy) between the basal planes of gibbsite and muscovite. In contrast, no film growth was observed at pH 9–12 where the solutions were supersaturated with respect to gibbsite. These results indicate that adsorption and accumulation of aqueous Al(III) species (i.e., Al3+ and AlOH2+ at acidic pH) is a critical step for the formation of secondary minerals on the negatively-charged muscovite surface.

Keywords: Mica, Nucleation, Epitaxy; AFM; CTR/RAXR; X-ray Reflectivity

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Permalink: https://www.hzdr.de/publications/Publ-28458
Publ.-Id: 28458


Transport properties of Cu-doped bismuth selenide single crystals at high magnetic fields up to 60 Tesla: Shubnikov–de Haas oscillations and π-Berry phase

Romanova, T. A.; Knyazev, D. A.; Wang, Z.; Sadakov, A. V.; Prudkoglyad, V. A.

We report Shubnikov-de Haas (SdH) and Hall oscillations in Cu-doped high quality bismuth selenide single crystals. To increase the accuracy of Berry phase determination by means of the of the SdH oscillations phase analysis we present a study of n-type samples with bulk carrier density n ∼ 1019 − 1020 cm−3 at high magnetic field up to 60 Tesla. In particular, Landau level fan diagram starting from the value of the Landau index N = 4 was plotted. Thus, from our data we found π-Berry phase that directly indicates the Dirac nature of the carriers in three-dimensional topological insulator (3D TI) based on Cu-doped bismuth selenide. We argued that in our samples the magnetotransport is determined by a general group of carriers that exhibit quasi-two-dimensional (2D) behaviour and are characterized by topological π-Berry phase. Along with the main contribution to the conductivity the presence of a small group of bulk carriers was registered. For 3D-pocket Berry phase was identified as zero, which is a characteristic of trivial metallic states.

Permalink: https://www.hzdr.de/publications/Publ-28457
Publ.-Id: 28457


High-Field Magnetization Study of R2Fe17N2 (R = Ho and Er) Nitrides

Tereshina, I. S.; Tereshina-Chitrova, E. A.; Pelevin, I. A.; Doerr, M.; Law, J. M.; Verbetski, V. N.; Salamova, A. A.

The structure and magnetic properties of the nitrided compounds R2Fe17N2 (R = Ho and Er) are studied. The type of crystal structure Th2Ni17 is preserved upon nitrogenation, and the relative unit cell volume ΔV/V increase exceeds 6%. Magnetic studies are performed in fields up to 60 T at 4.2 K on aligned powder samples. Field-induced spin-reorientation (SR) transitions are observed in the M(H) curves of R2Fe17N2. Unlike the parent R2Fe17 compounds, where the magnetization increases in steps as the field grows stronger, 2Fe17N2 demonstrate a gradual increase in magnetization. It is indicative of the change of the SR transition from first to the second type. Extrapolation of magnetization curves to the theoretical value of magnetization in the forced ferromagnetic state yields the coefficient of the inter-sublattice R–Fe exchange interaction. The inter-sublattice exchange is found to decrease upon nitrogenation.

Permalink: https://www.hzdr.de/publications/Publ-28456
Publ.-Id: 28456


MsRi-CCF: Multi-Scale and Rotation-Insensitive Convolutional Channel Features for Geospatial Object Detection

Wu, X.; Hong, D.; Ghamisi, P.; Li, W.; Tao, R.

Geospatial object detection is a fundamental but challenging problem in the remote sensing community. Although deep learning has shown its power in extracting discriminative features, there is still room for improvement in its detection performance, particularly for objects with large ranges of variations in scale and direction. To this end, a novel approach, entitled multi-scale and rotation-insensitive convolutional channel features (MsRi-CCF), is proposed for geospatial object detection by integrating robust low-level feature generation, classifier generation with outlier removal, and detection with a power law. The low-level feature generation step consists of rotation-insensitive and multi-scale convolutional channel features, which were obtained by learning a regularized convolutional neural network (CNN) and integrating multi-scaled convolutional feature maps, followed by the fine-tuning of high-level connections in the CNN, respectively. Then, these generated features were fed into AdaBoost (chosen due to its lower computation and storage costs) with outlier removal to construct an object detection framework that facilitates robust classifier training. In the test phase, we adopted a log-space sampling approach instead of fine-scale sampling by using the fast feature pyramid strategy based on a computable power law. Extensive experimental results demonstrate that compared with several state-of-the-art baselines, the proposed MsRi-CCF approach yields better detection results, with 90.19% precision with the satellite dataset and 81.44% average precision with the NWPU VHR-10 datasets. Importantly, MsRi-CCF incurs no additional computational cost, which is only 0.92 s and 0.7 s per test image on the two datasets. Furthermore, we determined that most previous methods fail to gain an acceptable detection performance, particularly when they face several obstacles, such as deformations in objects (e.g., rotation, illumination, and scaling). Yet, these factors are effectively addressed by MsRi-CCF, yielding a robust geospatial object detection method.

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Permalink: https://www.hzdr.de/publications/Publ-28455
Publ.-Id: 28455


Element Selectivity in Second-Harmonic Generation of GaFeO3 by a Soft-X-Ray Free-Electron Laser

Yamamoto, S.; Omi, T.; Akai, H.; Kubota, Y.; Takahashi, Y.; Suzuki, Y.; Hirata, Y.; Yamamoto, K.; Yukawa, R.; Horiba, K.; Yumoto, H.; Koyama, T.; Ohashi, H.; Owada, S.; Tono, K.; Yabashi, M.; Shigemasa, E.; Yamamoto, S.; Kotsugi, M.; Wadati, H.; Kumigashira, H.; Arima, T.; Shin, S.; Matsuda, I.

Nonlinear optical frequency conversion has been challenged to move down to the extreme ultraviolet and x-ray region. However, the extremely low signals have allowed researchers to only perform transmission experiments of the gas phase or ultrathin films. Here, we report second harmonic generation (SHG) of the reflected beam of a soft x-ray free-electron laser from a solid, which is enhanced by the resonant effect. The observation revealed that the double resonance condition can be met by absorption edges for transition metal oxides in the soft x-ray range, and this suggests that the resonant SHG technique can be applicable to a wide range of materials.We discuss the possibility of element-selective SHG spectroscopy measurements in the soft x-ray range.

Permalink: https://www.hzdr.de/publications/Publ-28454
Publ.-Id: 28454


Ultra-fast annealing manipulated spinodal nano-decomposition in Mn-implanted Ge

Liu, C.; Hübner, R.; Xie, Y.; Wang, M.; Xu, C.; Jiang, Z.; Yuan, Y.; Li, X.; Yang, J.; Li, L.; Weschke, E.; Prucnal, S.; Helm, M.; Zhou, S.

In the present work, millisecond-range flash lamp annealing is used to recrystallize Mnimplanted Ge. Through systematic investigations of structural and magnetic properties, we find that the flash lamp annealing produces a phase mixture consisting of spinodally decomposed Mn-rich ferromagnetic clusters within a paramagnetic-like matrix with randomly distributed Mn atoms. Increasing the annealing energy density from 46, via 50, to 56 J cm−2 causes the segregation of Mn atoms into clusters, as proven by transmission electron microscopy analysis and quantitatively confirmed by magnetization measurements. According to x-ray absorption spectroscopy, the dilute Mn ions within Ge are in d5 electronic configuration. This Mn-doped Ge shows paramagnetism, as evidenced by the unsaturated magnetic-field-dependent x-ray magnetic circular dichroism signal. Our study reveals how spinodal decomposition occurs and influences the formation of ferromagnetic Mn-rich Ge–Mn nanoclusters.

Keywords: ion implantation; flash lamp annealing; spinodal decomposition; Ge–Mn nanoclusters

Permalink: https://www.hzdr.de/publications/Publ-28453
Publ.-Id: 28453


Femtosecond resonant magneto-optical Kerr effect measurement on an ultrathin magnetic film in a soft X-ray free electron laser

Yamamoto, S.; Kubota, Y.; Yamamoto, K.; Takahashi, Y.; Maruyama, K.; Suzuki, Y.; Hobara, R.; Fujisawa, M.; Oshima, D.; Owada, S.; Togashi, T.; Tono, K.; Yabashi, M.; Hirata, Y.; Yamamoto, S.; Kotsugi, M.; Wadati, H.; Kato, T.; Iwata, S.; Shin, S.; Matsuda, I.

Time-resolved magneto-optical Kerr effect (MOKE) measurement was demonstrated on a sample of the Au/Fe/Au heterostructure with the Fe layer of 0.35nm thickness under Fe M-edge resonance condition. An ultrabrilliant free electron laser (FEL) in the soft X-ray range was facilitated for the detection of transient signals of resonant MOKE from the ultrathin Fe film. A variation in the Kerr rotation angle was successfully observed on the femtosecond timescale. This technique enables us to reveal the transient magnetization dynamics of such a-few-monolayer magnetic films, which promote the development of spintronic devices.

Permalink: https://www.hzdr.de/publications/Publ-28452
Publ.-Id: 28452


Neugier trifft Know-how: Erfahrungsaustausch für Wissenschaftlerinnen zu ERC und Marie-Sklodowska-Curie Maßnahmen

Lederer, F.

Neugier trifft Know-How:
Erfahrungsaustusch für Wissenschaftlerinnen zu ERC und Marie-Sklodowska-Curie-Maßnahmen

  • Invited lecture (Conferences)
    Neugier trifft Know-how: Erfahrungsaustausch für Wissenschaftlerinnen zu ERC und Marie-Sklodowska-Curie-Maßnahmen, 12.11.2018, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-28451
Publ.-Id: 28451


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